Hi,
My suggestion is to put in the pump with a bypass valve around it, from inlet to outlet. Then you can open that valve to fill the rear tank with the front pump. You can gravity fill the front tank, then pump the rear tank full as you want it. Then you can use one or both pumps to supply fresh water for RV use, and have a powerful shower if desired (say on the last day when you will be dumping the excess water anyway).
In this way, you could fill the front 40 gallon tank, then put away your garden hose, and then pump 25 gallons into the back tank, and reduce your hitch weight significantly, while still having 40 gallons on board total (for the lightest tow weight). Or fill the rear tank, then the front one, and carry 65 gallons.
Yes with only a kayak to offset the heavy hitch weight, you can use the extra water behind the rear axle. I agree that putting it inside is bad, not just a tripping hazard, but also weight below the floor is better than weight above the floor, due to center of gravity issues.
Putting some 3/4" marine grade plywood under the tank, and unistrut or something strong to support it will keep that 250 pound (full weight) tank in place. 3/8" allthread in all for corners is strong enough to carry the weight, then some.
Fred.
