I guess some of the fast axle SBUs can go 60mph, but that may be near redline on flat ground. And as we've discussed elsewhere that's going to take maybe ~200hp plus.
I don't get the impression that people cruising at 55-60mph worry about 55 mph rated tires, especially if way under the weight rating. Much more risk is probably taken by running fast at low air pressure.
As far as camper size, a big SBU doka like the 2450 "dinohunter" had a camper that was about 8 feet long, I believe. That's why couples have mog campers, and families have RV's and trailers.
A double cab Tundra or F250 pulling a high clearance trailer can go more places than something like Ecoroamer. A some point designing to cram everyone into a single 4x4 vehicle has no benefit.
