I've owned an '85 Toyota RV for over 25 years and have come to some conclusions:
The Sunrader has the best shell or coach area for longevity because its made of fiberglass. But they can and do leak around windows and any roof penetrations and have their own repair problems because of the fiberglass and wood wall construction and the composite floor construction.
The older Toyotas, made before 1986 had dual tires in the rear but only had a half ton axle which was susceptible to axle failure and often caused major damage to the rear of the RV when the axle failed. A government recall was issued for Toyotas made with the old axles and many were upgraded to a full floating one ton axle. After 1986 all Toyota RVs had the proper upgraded axle.
Wood framed Toyota RVs are fine if they are kept in a garage or somehow sheltered from rain and snow. Always look under the cabover mattress and the ceiling for water stains which could indicate rot in the walls or ceiling. This sort of damage isn't particularly difficult to repair for someone with average carpentry skills but is extremely fussy and, for some owners, a daunting task. To have rot repairs done by a shop would easily be way over the cost of the RV itself.
The four cylinder versus six cylinder debate still goes on at the couple of Toyota RV sites that I visit. The 22R and the 22RE four cylinder engines are great pieces of machinery and easily last for 150,000 to 200,000 miles with normal care. They are woefully inadequate for hauling around the coach section of the RV but most owners just settle into a life of about 55 mph or less on the highway. Mountain passes are no problem but one will be driving in the slow lane at about 25 to 35 mph on the uphills. The V-6 engine has more power but is needs quite a bit more maintenance than the four. Having the valves adjusted on the V-6 can run near $1,000 at some shops and this job MUST be done at regular intervals for long engine life.
Gas mileage in either the four or six varies by only a mile or two in most cases. Either way, driving at about 55 mph will net you between 14 and 16 mpg with either engine. Any seller who claims that they get 18 to 20 mpg, or more, is lying or has done all their driving downhill with a 20 mile per hour tailwind all the time wherever they go.
I like these little RVs. They are easy to drive, have all the basic amenities and usually get lots of attention whenever you stop. Like Jester said everything depends on how well the thing was taken care of. The newest Toyota RV (last year of manufacture was 1994) is still a 22 year old unit with all that implies like belts, hoses, transmission, engine, drivetrain, rear end, etc. Good units are still out there but expect to pay about $6,000 for one in good shape. Some of the newer models sell in the $12,000 range and up if they're in beautiful condition and have been garaged and have low miles.
As for my own '85 Toyota Dolphin, I've completely rebuilt both sides, the rear and the cabover section of the coach to better than new after finding rot in those places in the wood framing. After retiring from 40 years of building and repairing wooden boats, I didn't find the job particularly difficult, just fussy and a bit time consuming. I just looked at the job as another rotten boat project.
John