RonHr,
Yes just sitting is bad. Bottom line in most cases tires will age out before worn out. Tread wear on older tires is not a good indicator.
Definitely learn how to read tire codes as mentioned above.
I remember you have been looking at 1999 thru about 2003. Tires should have been long gone on the ones that were OEM. However still look at date codes. By chance if Goodyear G-159's are on the coach insist they be changed. I mentioned them earlier in a thread you posted.
Goodyear, Michellin, Toyo all make good tires. There is a guy down here parked in the same area I'm in with a Newell $$$$$ and he runs goodyear on the front and some of the wall Chinese tires on the rear to include his tag. The off wall thing is not for me. I've had a right front tire blow out in the past. I'd rather land on a carrier NORDO on a rainy night with a sevrely pitching deck that go thru that experience.