It is beyond a PITA to change the back tires with a dually. Forget it! Call Good Sam and let the guy worry about it. It is good to have the spare he can use, since he probably won't have his own that fits for lugs or whatever.
It is the worst when it is the inner that is flat. Of course that will be the one that has a nail in it! :( BTDT.
Naturally, you have the spare on the back bumper under a bag with a nice shiny metal cover around the whole thing. Huge PITA to check if it has any air in it from time to time, so for sure it will be flat too once you manage to get it out of there (in the rain of course).
Rving is fun if you don't weaken!