[sourdough]

As was pointed out, you are making the mistake many first time buyers do; comparing the most optimistic, unrealistic numbers to make the vehicle fit the trailer that you love. Reality, unfortunately, many times is different.

Your van can POSSIBLY tow up to 3500 lbs. Look inside the driver door of your van and find the payload. A Sienna is a light weight mini van - a grocery getter, not a tow vehicle. Since you are looking at a bunkhouse model I assume you have kids.

The listed dry weight of the 175bh according to Keystone is 3255 with a gvw of 4500 lbs. You need to use 4500 since you will never see the 3255 except on paper. With 2 adults and children you will carry quite a load - you can't keep from it unless you don't go camping.

Back to payload; you will have the adults, kids and all your gear in the van. That number has to be deducted from the payload listed on the door; lets just say 600 lbs. conservatively. Now you have to take the hitch into effect; say 100 lbs.; now the tongue weight...at 4500 lbs. figure a tongue weight of 525-550 conservatively. Adding those up you have about 1250 vs whatever the payload is on the door. In addition, the tongue weight is over the limit of your hitch, and could be by a considerable margin.

Keep in mind that the Sienna was never meant to be a real "tow" vehicle, it has VERY marginal towing capability. The suspension is made to give you a comfortable ride around town, not to control 4500 lbs. swinging in the wind behind you.

All that said, you can probably surmise that I would advise against it. It would be a bad choice IMO and compromise the safety of you, your wife and family. Buy that used 1/2 ton and make yourself a much happier, and safer, camper. JMO