Thx.you can use 1/8" wall aluminum for the bottom frame, but for the top part that holds your roof, doors, etc 1/16 or thinner tubing is more than enough. I am working on a velo top that is using 3/4" square tube with 0.040" thin walls Ten feet of this is about 1.5 lbs in weight
I think that is what I have a huge stock of in my garage from a camper project that I never finished (King of unfinished projects) -- up in rafters now so cant check it till I go to use it. I also have some 1/8 bits should I need, maybe the front and rear wheel pieces need 1/8 as they will take a pounding.I would use 1/16, but no one stocks it in that wall thickness locally.
Thanks for your interestIf you need tow motors on a single drive wheel, think about using a hub motor and a single reduction ration 415 chain drive. That would give you a low gear for hill climbing. Ya I know ....chains are a headache at times. But if they don't shift it is not as big of a problem.
I thought you might be interested in this Open Source trike project just in case you haven't seen it before: opensourceecology.org/wiki/Velocar