I like the way you think, I also pull a heavy load with a 116 Ultimate Suite Okanagan. Went from a f350 to a f550 with a service body. Very happy with the combination now, but a year ago we had some serious problems with the ring gear. Ford ended up installing a new short block to solve it but at the time we were also considering going that route, I think a service body would do better than the typical box considering all the extra space for stuff. The engines you get with those rigs will give you way better economy and torque for the long hills. I don’t think a 4 X 4 would be in the mix though, the height would make it look a little off.