I got 4x 46 gallon water tanks. The dimensions are not exactly what I hoped for, but I think I can squeeze them in. I originally wanted to hang them centerline on the frame cross members but I can’t wedge them in there with the luggage bay. I’d have to cut a big hole somewhere.
So, I’ll make lemonade from the lemons and build a set of support brackets for the ends of the tanks, and some heavy channel between them. I’ll be able to insulate the tanks with 2″ of foam. I’ll probably get some tank heater panels too.