I could see keeping a used tire that fits just in case the roadside assistance truck can't find your size. This will give you the ability to limp to a better place to shop for the tire. You will then have to pay to mount it twice though.
I don't want to carry $500 worth of tire around for 7-10 years just to have it age out, so I don't bother. To some, that is good insurance.
Another option people forget or don't realize is that Ford provides roadside assistance to you for the duration of your warranty. They will send a repair service to you. You can buy the tire then. Ford will also assist you after the warranty but you pay.
I received a complementary membership to Coach Net with the new MH. When it came time to shop, I discovered that I have roadside assistance from Ford, so I went with that.
In this day and age with mobile data, cell phones and all that, I think I could track down a roadside service truck as quickly as the next guy. The service will be on my dime, though. So far, I'm ahead one year.