On our Lexi the storage compartments are a one piece moulded pod type affair. Seems to be at least 3/8 to 1/2 inch thick, very sturdy and stable. Super easy to clean out, and never have to worry about water or moisture inside causing any type of rot.
Have had to leave campgrounds in the rain, and just throw wheel blocks, hoses, electric cable, all soaking wet, and never worry about it. Just clean the moisture and mud out the next dry day.
As far as weight, I carry tools in one, compressor and 12 ton bottle jack in another, Weber grill, folding table, wheel blocks (40 of em), and have never noticed any bouncing around of contents, and stability and strength is just fine.