Bill:
...you may want to consider lining up batteries foreword of the wheel wells (maybe 2 or 3 per side) ? This would work if the Bigfoot's tub wall shape is vertical up to camper wings.
Pad 5 sides the batteries with high density foam; use a custom density foam under the batteries to account for bed bounce/shock.
A long bed truck would afford more foreword-of-wheel-well room to line batteries up.
The trick is getting all the dimensions correct and account for foam (foam would have a dual purpose: 1) shock absorbency; 2) insulation ). And, building a set of quick connect/disconnect battery cable umbilicals.
The only concern I would address would be "camper tub pivot". But this could be kept in check with camper tub guides up close to the truck's bulkhead....
*locating the batteries low to the ground would lower the rig's center of gravity, and would put more weight on the truck's front axle, better axle-to-axle weight distribution