I agree that your tires should be inspected by a qualified truck tire shop. I ran a previous set of Michelin XZA's (on our previous motorhome) into the tenth year. They looked great on the outside, but when unmounted they were cracked all thoughout the inner casing. We were definately riding on borrowed time. In your case you may be able to get another year or so out of them.
The tires on our current unit are dated late 2005, 7+ years old. These are XRV's and are showing cracking on the sidewalls. The previous owner spent winters in Florida and never covered the tires.
I am in the process of replacing them. I have ordered 6 replacements using the FMCA Michelin Advantage Program and saving a substantial amount of cash. The discount is nearly 50% of retail, and a couple hundred per tire under the street price. The saving for my size is about 45% less than the best price I can get on Goodyear.