Jim,
Typically, motorhome tires typically never wear out; They rot out first, posing the risk of a potential blowout on the highway. We have an unscientific rule of thuimb here in the forum that 7 years is when one should be looking for replacements. There are arguments about whether temperature &/or storage conditions affect that duration, so the real usable time might vary.
Our tires were 10 years old. We didn't use the coach in 2011 or IIRC the latter half of 2010, but I'd have bought new tires before making a trip, as I just did. I crossed my fingers all the way to the tire dealer, and let my driver know she should take it easy (i.e. not go too fast) and not make any sharp movements maneuvers.
When those "old" tires came off, they looked in pretty good condition. Only slight treadwear, and no signs of problems on the walls or inside. Who knows when they might have popped, but I feel a lot more comfortable with the new ones installed.