Thanks for the reply o1marc.
Is it possible to overload these? My compartments are probably like yours. I have two located just in front of the rear wheels, well actually its one compartment with two doors and one just behind the wheels for a total of three compartments on each side. Being that the front ones are quite long (about 120" long) they could potentially hold a very large tank. I'm looking at a 70 gallon tank for each side to hold grey water. Water weighs about 8.8 lbs per gallon so that's potentially 600+ lbs. The front half of one compartment will hold the energy storage, i.e. batteries, inverter, and so forth. I just wanted to make sure I didn't need to brace these compartment with extra steel bracing for all that weight. It's not exactly band instruments or football gear, which is likely what was intended to be hauled in there!