My 30gal will fit where the spare tire is, but I have not found another spot I liked for the spare tire. Back door does not work as it obstructs the door from opening enough to be bothersome... and I load dirt bikes, mtn bikes, and jetskis in my van, and need max door opening clearance. Thought about putting the spare on the roof, but that requires a rack to be intalled, and adds more wind resistance which the van does not need. So as of right now I just put the 30gallon on the floor between back seat and drivers seat. It has on/off and quick connects, so if 2 people needs to sit in the back seat I can remove it in under 5mins. But I want to get the tank out of the van and mounted under. Just takes up too much space.
I did some measuring and I can get a 18-20 gallon custom made tank to fit under my back seat. Which is my next best option, but I like the storage I have under the seat now. If anyone has installed tanks under there vans any and all ideas are GREATLY appreciated! I thought I read sportsmobile had a undervan side mounted grey water tank, but I could be mistaken. 10-20 gallons is low for my needs, 20-30 is good, 30-40 is ideal.