I would be leery of 1/8" thick tanks, water is heavy and sloshing around could over power the lighter material. 3/8" thick seems a bit overkill, but much better than 1/8". If they make a 1/4" wall thickness, I would think that would be sufficient.
03 Silverado cclb 3500 drw, D/A, Reese 22k hitch
07 Alfa SeeYa Gold 30RL,2 slides,power everything