For what it's worth: we wanted a spare tire onboard so that a Roadside Assist call would only require a professional with the right tools to safely remove the flat and install the spare. Call me a wimp but I don't want to face changing a tire on our 20,000 pound Class C in the dark with freeway traffic roaring by and the Saintly Spouse offering helpful suggestions from the sidelines!
We were lucky that all six tires and rims are identical. We saved a bunch of $$ by asking our Tire Guy to call around and find a compatible steel rim used at a wrecker. It turned out that a new rim cost almost as much as the new spare tire itself. I think my total expense was $430.
I know it should be firmly mounted in "The Basement" storage compartment but the thing is so heavy and the rubber so sticky that it hasn't budged a bit so far.
-Grouchy