If you dig back through the Forum, you will find the first part of this observation at:
http://www.keystonerv.org/forums/showthread.php?t=4784
Here again, the following Disclaimer applies: All views and observations expressed are personal and based upon examination of one particular unit of the Keystone Alpine 3640RL. Etc., etc., etc. Also, I would not recommend anyone whose Keystone One Year Warranty is still in affect to even think about doing any of this type work! I also know that one of our members formerly worked at a Keystone RV dealer in the Repair Department. I would welcome his comments to these posts and hope he will add his observations.
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If you read the first part of this observation, you will know that I am in the process of adding UltraHeat Tank Heaters to my Alpine. The second part of this installation involves something that I know there will be gasps of surprise and feelings of doom, so I might as well get it over:
I used a box cutter to cut the coroplast twice to remove a six foot section.
I cut the aluminum-lined bubble wrap only on one side and wrapped it over the axle to keep it out of the way.
OK, anyone pass out? Still here? Good. Hey, it's not the end of the world. I'll tell you how to fix and seal the cuts up later. Just look at the good information you are getting! Apologies to our Canadian members if you don't mind for brevity (Ha! As if I could be brief!) I only utilize Imperial measurements and drop the Metric. Also, because of the limit of attached pictures, I have broken this post into two parts. (Need to set up a Photobucket account!) A different post on Modification will discuss the UltraHeat tank heaters.
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Because of the gas supply iron pipe running alongside the port side of the underbelly, I chose to cut a six foot section of the coroplast out from about the forward edge of the door to the area above the forward axle. I removed the bolts holding the coroplast on the I-beam on the starboard side. I gently pulled the edge of the coroplast down to shine a flashlight inside to check my location. Then out came the box cutter and the slicing began! I first cut along one channel of the coroplast, not all the way through, for both entire widths of the underbelly. I then returned to the cut on the starboard side and gently pulled the coroplast down for the final cut. I then removed the bolts holding the gas pipe in that area, gently pulled the pipe down, and cut the coroplast above it. Once that was completed, I cut the aluminum-sided bubble wrap along the forward side and wrapped it around the forward axle to keep it from blowing in the wind and form a wind break for me.
All I could do was shake my head; what can I say? There was a 4' wide piece of fiberglass insulation stretching from immediately behind the fresh water tank forward to below the Gray2 tank. The Gray2 tank is only 32 gallons and stretches from one side I-beam to the other, which means it is a very shallow tank. There was probably at least 4" of space between the bottom of the tank and the top of the fiberglass. The R-7 fiberglass did not reach the I-beams but fell about a foot short on each side. The bottom of the Fresh Water tank was deeply nestled in the fiberglass but open along each side near the I-beams. Again, this insulation stopped immediately forward of the Gray2 tank and immediately aft of the Fresh Water tank. As said before, I am not an "insulation engineer", but I believe I know enough about insulation to say, this single sparse pad of R-7 insulation holds very little insulating value when compared to the vast open area available for cold air intrusion and conduction presented by the rest of the underbelly. (See Looking_Aft.jpg) In this picture, one can see the furnace ducts and cross-bracing along with a darkness of "nothing". Note the dusty area of the aluminum-coated bubble wrap versus the shiny area. Again, I found about a half-cup of water in the belly primarily on the bubble wrap. This has pretty much convinced me that the moisture is condensation from warmer air in the void area of the belly being cooled to drop its moisture content which pools on the bubble wrap. Note how the moisture has been diverted by the discarded cable strap in the picture.
Looking forward from my "belly hole", I can see the maze of ducts descending from a fitting on the lower sub-basement ceiling. (Forward.jpg) The drain for the Gray2 is to the left along with the duct for the kitchen furnace vent. (The black ribbed pipe is something I added two years ago to try to prop this duct from being pinched by the power cable.) The two other insulated ducts pass to the starboard side and run back to the two vents in the living area. The aluminum duct is from the forward duct that supplies warmed air on the Black and Gray1 tank valves and ends with an open duct directed at the Gray2 tank valve. (Gray2_heat.jpg)
That is it – that is the "heated tank area" of my Alpine Arctic R-37 Package! Two paltry pieces of R-7 insulation (front and rear tank areas) along with a 2.5" duct venting to the three valves.
Two years ago, I was trying to solve a problem with my fresh water fill. During this process, I stuck my hand and camera down a hole beneath the pantry and took the attached picture. (Port_side.jpg) At the time, I didn't know how to interpret this photograph, but now I fully understand it. The darkness to the right is the I-beam. The area is specked with construction dust and bits. The shiny black to the upper left is the Gray2 tank. Upper center one can see the sensors on this tank (bolts with nuts) and to the right of those the ribbed fresh water fill line and the associated fresh water tank vent line. To the lower left, the furnace duct for the kitchen heating vent passed under the Gray2 tank. Various power wires lay in the foreground. The dusty black cable is the shore power cable coming from the rear of the Alpine. However, from the back, one can see a white Pex pipe passing under the shore power cable. That Pex pipe is the fresh water feed line to the Shur-Flo pump! And it is pressed onto the bubble wrap/coroplast by the shore power cable right next to the I-beam. Neither well insulation nor isolated! In the far background, one can barely make out the toothed slide mechanism for the kitchen slide.
The toothed slide mechanism can be better seen in Slide_gear.jpg. Note, the Fresh Water tank to the left and the Gray2 tank to the right separated by a cross-beam member. The R-7 insulation was pressed beneath this cross-beam member providing a large uninsulated volume between the tanks.
I’m not sure if I should look for the inferior workmanship items or just turn my back and hope it doesn’t happen to my 318. This post has given me incentive, preventative maintenance lives. Thank you for your time and trouble. 
Things are always good here.
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