Hi, you're plan sounds great! We actually did have some issues with the weight on our bumper and on the back tow hitch. We carried 2 spare tires and after maybe 8K miles, with a lot of bumpy unpaved roads, our bumper was almost completely "ripped" off of the RV. We posted about that incident and our repair on our blog you found. ALSO, we discovered that our cargo carrier acted as a lever of sorts and damaged the back of our RV. Basically, the Toyota chassis ends a foot or so behind the rear wheels. Winnebago extended the chassis a few feet with inferior materials. Right at the joint where the Toyota part ends and the Winnebago begins, it buckled. On both sides. Yep, the two beams on either side extending beyond the rear wheels, bent from the weight and lever action of the cargo carrier. We discovered this after prob 12K miles or so? We were on our way back and I think in Tennessee? Adam realized the back of the RV was sagging dangerously. We took the spare tires off the back bumper and removed the cargo carrier and stowed it and it's contents inside for the rest of the way back. We carried 2 folding chairs, our telescoping ladder (20lbs?) and our little folding stainless grill (15lbs?) and a big rubbermaid storage bin (40lbs?). For some of our remote driving, we also carried 2 X 6 gallon jugs of gasoline. It didn't seem like much, but I guess it was. We only recently got it fixed by straightening the areas that were buckled and welding supports to reinforce those areas. If you plan on weight on the tow hitch, welding supports and beefing up the rear beams is not a bad idea before hand, especially that area where Toyota stops and Winnebago begins.
Cheers! and safe travels