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Old 05-03-2013, 02:45 PM   #1
Bigrig E
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Coroplast

Was wondering what the purpose of this stuff is. and has any body done away with it? Also if you cut an access hole and dont replace it and go down the road what will happen? could air get in and pull the rest down?
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Old 05-03-2013, 03:33 PM   #2
CincyGus
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Depending on what you believe, I've heard the following:

It's a vapor barrier to keep rain, dirt, etc from getting in the bottom of your trailer as you go down the road.

It helps insulate the floor of your trailer and keep the insulation dry.

It helps with gas mileage by making the bottom of the trailer more aerodynamic.

If you need to cut a access panel, just do soin the shape of a "C" and use gorilla tape to seal it back up. I've seen others do this without harm. I don't think I would want a open cutout without replacing it as you mention, it might grab air at 65mpg and pull the whole thing down.
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Old 05-03-2013, 05:23 PM   #3
MIKEPATC
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Frankly, I believe all the previous reasons for the underbelly. I would never do away with it.
To gain access:
Your best choice would be to cut an access hatch. Take a couple of the screws that hold the underbelly out and wedge the underbelly away from the frame just enough to be able to shine a light in to see where you are at. Fish a measuring tape into that opening to see how far from the frame edge you want the hatch to be.
When you make the first cut, which should be perpendicular to the frame on the rear side of where you want the hatch, wedge it open and shine the light it to see where you are at.
Figure out where you want the cuts that were parallel to the frame for the sides of the hatch using that info. If you are in doubt, make the hatch bigger than you need it to be and the area you need to work on should be in it somewhere.
Be careful to make a shallow cut as to not penetrate your holding tanks. Use a retractable utility knife with the blade extension set to match the belly thickness as closely as possible.
Create a wood frame for the hatch. Use stainless screws and pressure treated fence board for the frame around the opening. Make the hatch with the "hinge" side towards the front of the trailer. In case you forget to put the screws back in, air flow will push it closed ... in place of trying to rip it off.
Just be sure not to use screws that are longer than the combined thickness of your board plus the underbelly to be sure you don't penetrate any tanks.
If you decide to take the cover off to access the tanks be sure to take note of the screws near the tanks. Some of them are shorter than the rest to keep from going through the tanks.
Be careful to note where the shorter ones are when you remove them so that you can reinstall them in the proper place. If you don't it's all too easy to put the wrong one in and put a hole in one of the tanks and that will really be a problem.

If you think you need to take the underbelly down and put it backup, make sure you have a buddy or two that will suffer with you while you take it down and put it back up. Failing that have a couple of jacks and a 2x4 to hold it in place as you attach screws to hold it.

Enjoy
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Old 05-03-2013, 05:31 PM   #4
Bigrig E
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Well that certainly answers any questions I had or could have had awesome info thank you both.
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Old 05-05-2013, 05:47 PM   #5
diugo
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I think one of its most important purposes is to keep rodents out.

If it's a small simple access hatch---and one you might open again in the future---consider securing it with a few cable ties instead of Gorilla Tape.

P.S. Never knew it was called coroplast, thanks for that!
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Old 10-01-2013, 09:09 AM   #6
Bob Landry
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As thin as tape is, I would tape up an opening with Gorilla Tape and if I ever needed to access that particular area again, I would simply cut through the tape along the same cut, do the work, and tape it up again.

I haven't looked inside mine yet, but I would think that the coroplast also creates somewhat of a "plenum" to direct warm air from the furnace to the tanks in cold weather. It is secured at the factory with 5/16" self tapping screws, so I think I will probably drop it instead of cutting. Either way should be fine.
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Old 10-01-2013, 10:58 AM   #7
therink
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I recently had to service my tank valves (a whole other story)and cut a square opening the size needed to access both valves. I went to a sign shop and they gave me a 2' x 2' piece of black coroplast. I then installed the new piece over then opening and then secured it with 3/4" self tapping screws and then sealed edges with Gorilla tape. I now have a nice hatch for future entry.
To answer Ops question, I would not remove cover or leave open hole for reasons stated above.
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Old 10-01-2013, 02:26 PM   #8
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Pretty much everything Cincygus said, except insulation. Coroplast basically has no insulation qualities, and the aluminum-bubble-wrap doesn't add much either. But the coroplast also supports the heating flexible ducts, the wiring, and the Pex piping. If you look in my posts in Repairs and also in Mods, you will find lots of pictures of the underbelly without the coroplast. I installed tank heaters on our Alpine and also properly insulated the underbelly. Once installed and insulated, I reinstalled the coroplast.

It would not be wise to permanently remove the coroplast.

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Old 10-01-2013, 02:27 PM   #9
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Coroplast is what they use on yard signs, never knew they used it in campers.
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Old 10-01-2013, 04:33 PM   #10
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Quote:
Originally Posted by geo View Post
Pretty much everything Cincygus said, except insulation. Coroplast basically has no insulation qualities, and the aluminum-bubble-wrap doesn't add much either. But the coroplast also supports the heating flexible ducts, the wiring, and the Pex piping. If you look in my posts in Repairs and also in Mods, you will find lots of pictures of the underbelly without the coroplast. I installed tank heaters on our Alpine and also properly insulated the underbelly. Once installed and insulated, I reinstalled the coroplast.

It would not be wise to permanently remove the coroplast.

Ron

Coroplast or any other material has an R factor (insulating value) it may be very, very low but it has one. The advantage of the covering, in this case Coroplast, across the bottom of the framing is that it creates a "dead air space" and that is where the insulating value is generated.

The principle behind Thermopane windows is the dead air space sealed between the two panes of glass not the two layers of glass.

I'd suggest leaving it in place.

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Old 10-01-2013, 04:55 PM   #11
Bob Landry
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While I was exploring today looking for a way to run an additional 20A circuit, I discovered what is probably the most important function of coroplast. It supports the birds nest of wiring below the trailer. There's nothing underneath that even closely resembles an organized wiring harness.
There is a lot of open space between the floor and the coroplast, and if I were going to do any serious cold weather camping, I would seriously consider installing some fiberglass insulation.
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Old 10-01-2013, 05:29 PM   #12
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Quote:
Originally Posted by Bob Landry View Post
There is a lot of open space between the floor and the coroplast, and if I were going to do any serious cold weather camping, I would seriously consider installing some fiberglass insulation.
Bob-

Geo, our infamous Lord of the Underbelly, would agree with your finding. It is, essentially, a large and very poorly insulated air space. No one should think that Keystone's "insulated and heated" underbelly will keep the RV warm and cozy or offer much in the way of protection for the water lines when the mercury starts to drop.
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Old 10-01-2013, 06:00 PM   #13
Bob Landry
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Another question about Keystone's Arctic Package.. I didn't pull the coroolast back very far because I didn't wan to have to wrestle it back in place, bu I'm wondering if there is actually a heater duct directed below or do the tanks just get "heated" via the heat that radiates through the duct on the way to the registers. Has anyone every looked this far below the flooring to see what Keystone actually did?
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Old 10-01-2013, 06:20 PM   #14
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Bob,

There is a 2" heat duct routed from the furnace through the floor and between the gray and black tank on my Cougar. In the Springdale, that same 2" duct was routed between the gray tank (only had one) and the fresh water tank. I'm not about to speculate how well a 2" ducted hot air source will heat (prevent freezing) in what appears to be a minimally insulated space containing over 150 gallons of water (Gray, black and fresh).

Additionally, the 4" aluminized flex duct is not insulated and runs from the furnace through the floor and to the forward air plenum as well as a separate run to the main cabin floor register.

Realize, however, that the frame rails are not insulated and they are full of holes, so what little insulation is layered above the coroplast isn't going to effectively insulate much of the "dead air space" between the floor and the coroplast. If I remember correctly, Geo posted pictures of his "before" space. Pretty much the same construction techniques are used in all Keystone products so his pictures are representative of what is in your RV.
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