I made use of the spare on my motorhome on the last trip due to a rear tire giving up the ghost. (The tread separated and came clear off the tire. It wasn't a blow-out or a flat as the treadless tire still held air.) I had the "pleasure" of changing it on the shoulder of an interstate highway, which I safely managed. I could have called AAA, of course, but I think it would have taken longer overall--perhaps a lot longer--for them to get someone who could come and do the job.
If you feel secure in changing the front tire on a class C, there's no reason you couldn't as easily change one of the dually rears as well. It only requires a somewhat larger minimum jack rating (and you probably would want one higher than the minimum regardless for margin and ease of jacking) and, if it's the inner wheel, the temporary removal of the outer to get to the inner. The basic process and, at least on the Ford chassis, the size of the wheel and tightness of the lug nuts is identical.