Hi everybody,
I am new here. I just bought a VW LT31 from '96 partly build. I have some work to build it my way 
I was looking on the web for a watertank to put under the car frame and I didn’t find anything for this specific model but some for the T3 or T4… it might be a dumb question but are this kind of watertank universal ? Otherwise, where may I find some for a LT31?
Thanks in advance,
Zwor
Greetings!
The T3 might be similar body, although rear engined, the T4 isn’t even close.
Cheers!
Take a look here:
Is your car 1st gen (1975-1995) or 2nd gen (1996-2005). Easy to tell with pictures 
2nd gen is actually MB Sprinter with Volkswagen engines so aftermarket water tanks and other camper equipment for same era Sprinters should fit.
If it is 1st gen, even on the wiki page there are two manufacturers who made campers on that base. I have no information on those or how popular they would still be, would someone manufacture spare parts for them. My best bet is just measure a good spots for your tanks and buy generic ones that fit well.