I owned a 1988 Damon Escaper build on a true one ton Toyota dually chassis. It had a 22Re engine (2.4l) and an 4 speed automatic tranny. We could not use 4th gear, overdrive, unless going down a steep grade. We drove that thing over 45,000 miles in 6 years. We had a great time traveling around in it but I would never own one again.
The first big problem is that it weighed 6,000 pounds and the chassis was maxed out before I filled the tank with gasoline. The engine made 120 horsepower. The gas mileage was not great like some people claim. I got 12 mpg going 55 and 9 mpg when my daughter tried driving 65. When I got into big hills I was driving 45 mph turning 5000 rpm's in 2nd gear. Remember that Toyota NEVER built a single RV, they supplied just the chassis and the builders overloaded every one of them. Until 1988, the chassis that was provided did not have a full floating one ton axle, they had 1/2 ton axles with dual wheels that were actually just half ton wheels welded together, they were called foolies by the people that had the RV's. Those foolies would break the axles at the housing and the wheels would fall off. Toyota eventually gave one ton axles to every owner of an RV that was build on one of their chassis to avoid publicity.
The RV's rode like lumber wagons, cornered like a double deck3er bus, and were so underpowered that with a stiff headwind, you could not go over 50 mph. If it was hot outside, you cannot use the dash mounted air conditioning because the truck will over heat.
There are many people that have the romantic belief that these things are great, if you want to hear more, send me a PM and give me your phone number.