I also carry a mounted 19.5 tire in a lower compartment of my 2000 HR Endeavor. I have a 20 ton bottle jack in case the on board jacks could not be used and a 3 foot breaker bar with a heavy duty deep socket.
I have not had to change one on the road but have removed and replaced a couple in my driveway over the years. If it was an unsafe location I might call for help, but otherwise I could change it out myself.
It's harder to get the tire in and out of the compartment than it is to change it.
After removing the bad tire, I stand the new one up and sit down facing it with my legs around it, sort of like getting ready to give it a hug and lift it about 1/2 inch using my legs and arms to get it on the lugs.
Tighten up, lower rig, re-tighten and off you go....
The key is only having to lift it about a 1/2 inch. Just need enough room to slide the old one off.