Oh heck.... just drive 'em until they blow out, destroy your coach, maybe cause you to **** your pants, and then replace 'em....... hopefully you won't be pulled into the other lane of traffic in front of someone else, or be thrown down an embankment in the mountains running 65mph. No need to worry about the tires' age because even brand new ones will blow out.
We had perfect-looking tires that were checked for condition by a reputable tire shop when we bought my coach. The couple we bought it from assured me that they had replaced the tires 2 years before, so with all that, I had the tire shop air them up to proper pressure and took off on a 350 miles trip. Made it there, had a great time, headed out towards home feeling confidant in my first motorhome outing and about 40 miles from the campground on I-40, on a Sunday afternoon, towing an enclosed trailer with my Harley in it,........BOOOOMMM!!!! I limp onto the VERY narrow emergency lane, get out to see rubber spread out behind me and the inside of the fender well badly damaged. There we sat for the next 3 hours waiting for a service company to come replace the tire at a whopping cost of $1K for 2 tires and the service call. See, the inner dually blew out and took out the outer with it. Technician looks at all the other tires and says, you realize all these are 10 years old. The LOOK good, but in RV terms, they are old and that's what likely caused the blowout. Got home, replaced the remaining tires, all is looking good. Fast forward 2 months, we head out for a 400 mile trip. About 250 miles into it, .......you guessed it.... BOOOMMM! Brand...new...tire......... the tread came right off of it. Factory defect apparently, since Goodyear did make it right eventually. Also took out most of the components in the fender well when it blew. Wiring harness, tailpipe, generator exhaust, gas-filler neck,...oh, and, well, fortunately the propane line that was in the well survived. Another $800 for the only tire that could be found in the area....no labor because after the first blowout we got Good Sam Roadside Assistance. Spent the first day and a half of our vacation making repairs in the campground so we could actually get back home.
So yeah, moral of the story don't take tire condition OR AGE lightly. Of course, if you're comfortable doing it, then by all means, as I said at first.... just drive 'em till they blow! It definitely makes it interesting...kinda like gambling........