I think the beams will be stacked, with 2x2 sitting across them, running from c-channel to c-channel. The bottom supports made of 3"x6". Dropping the tanks from the bottom, with the last tank sliding in from the back. 18" deep tank between the axles. I will do cad soon.
I mainly came on here to say this. If I were to keep the rear bath, I could easily put a seat over the seat in the shower. A piece of corean could hang over the edge and make it a bigger seat.
Remember my truck, I plan to finally get it back tomorrow! $300 labor, $850 for parts. The parts normally would have cost $1700. All of that because I looked at a Prevost. I think I will keep my eyes on the road and not cheat on my AS.