When I upgraded our previous 2004 Mobile Suites 36RE3 from the OEM Goodyear G614s to 17.5" aluminum wheels and Michelin XTAs, I went ahead and bought 5 wheel/tire assemblies from Trailer Tires and Wheels. My thinking was that the spare was just as old as the tires I was changing out based on age, and if I DID have to make a tire change on a trip, I had a wheel/tire assembly that I could leave on the ground until I got the failed tire replaced to use as a spare.
It really didn't matter - the 17.5" Michelin XTAs were flawless. Never a problem with them. The new Mobile Suites came with 17.5" Goodyear G114s - I hope they give the same service that the Michelin XTAs did.
Rusty