And while you are doing the pan stiffening, check the top edges of those plastic cargo pans where they meet the inner coach wall structures to assure it's well sealed. I drove on a dirt road recently and had my cargo area plus everything in it covered in dust. A fair amount of dust also made it into the cabin. Upon inspection, there were several areas around the pans where I could see daylight plus a couple bigger gaps. I pulled everything out, cleaned my gear, removed the pan plugs, hosed the basement out, then sealed the top edge of the pan with silicone all the way around.
I don't think the weight I had in the pans had warped the edges, they just appeared to not have been installed flush. However, I can see how over time that weight in the pans could also cause gaps around the edges, whether you stiffen the floor or not.