Instead of spending the money on a spare, install a TPMS for less cost and most likely you will never need your tires replaced except when they age out.
When we first (2010) got our current coach we had to have both DS duals replaced after one blew out and took the other one with it near Carlsbad, NM. This was done using a CoachNet provided service company and they replaced both tires roadside with tires that were different than the old ones but only in that the tire model had been changed by Michelin who no longer made the old model. They were what we replaced the other four with two years later as they aged out. We have had a TPMS every since and absolutely no problems.