pnichols,
In support of your theory, our first motor home was very tiny, built on a Toyota chassis. The chassis and house combined weighed only 3600 pounds. On trips we added an additional 600-700 pounds. Total weight on trips never exceeded 4500 pounds. It had 6 "D" rated tires which after 12 years, still looked decent with only minimal tire cracking. I sold the rig in 2007 with those 12 year old tires with roughly 50,000 miles of use. Had I kept the rig longer, I would have gone a couple more years before buying tires.
It was stored indoors when not in-use, in the same bay my PC does today.
I too am not convinced I should be replacing tires so often. Our 9200 pound rig today with 6 "E" rated tires is not quite like our previous rig, but still has lots of vehicle weight-to-tire rating margin. But unlike yourself, I don't max out the tire pressure at 80 psi, solely to keep the ride softer.
The Old Rig
The Weight
The 12 Year Old Tires
