Michael,
Nice truck bro! Good to see you pulled the trigger on it. It looks nice already, and you could definitely set that up for your needs. I'd put a nice TM in it, and have a larger waste tank made and make sure you have auto pump out. You can stack two of those dehu's you have on top of each other. Just by eyeing it it looks like 3-4 of them may fit next to each other behind that back side door. You could put 3(or 6 stacked) on each side of the box truck, and then stack your fans in between for stability so what won't rock back and forth. The only thing you'd have to worry about is when you stop them falling forward, and you could put a wall of some sort. Or removable bars going across, something like an industrial strength tension rod.