Just a thought, what I did was when I had my tires replaced last month I kept the best inner dually for the spare. My RV is a 2008, but the date code on the tires were 2207, they were getting close to eight years old. The tires looked great but one started to get the small weathering cracks and for peace of mind decided it was time to replace all of them. The thinking behind keeping the inner tire was less exposure to UV light and it was inspected and deemed usable. I placed the tire in the pass thru bay and I feel I won't be at someone's mercy on a Sunday roadside service with a mismatch tire. With your coach being a 2009 and possibly your chassis being a 08 you might be getting close to replacing tires. I agree with others on just carrying the unmounted spare as the way to go.