In our crew cab truck with the 60/40 rear seat, we sometimes leave the 60 in place and put my tools etc on the floor and use Tupperware type plastic boxes with lids on top for our canned goods, liquid containers, and other weighty items on top and also on the 60 seat surface. The 40 is folded down flat as GW truck rear seats do for our large dog so she has plenty of room to stretch out. Putting the heavy items forward of the TC and low as possible moves a lot of weight (hundreds of lbs) off the rear wheels transferring it to the front wheels. Our totally optioned out 11'4" TC weighs 3872 lbs as shipped from Lance and the truck handles the weight fine doing this and has for over 70,000 miles now. Yes, you even gain more storage space if needed by removing the rear seat totally. However, we haven't found the need to do so as there's plenty of room for my large tool box and 3 large plastic storage boxes with lids in the 60 area and simply taking them out and putting them on our site when we need the back seat for guests. A couple minutes max and solves both needs!
Don't use see thru plastic boxes and it won't draw the itchy fingers while sitting on your site when you are gone away. Also, the covered boxes keeps the rain out and/or you can put a cheap plastic tarp over them. Where's there's a will, there's a way!