How willing are you to be stuck somewhere for a day or two because you do not carry a spare.
Like a Saturday evening in a remote area where a tire dealer is not nearby. Even if there is a dealer he may not carry the brand you want or have a tire at a price you want to pay. The absolute worst time to negotiate a tire purchase is when you are stuck on the road somewhere. You will be willing to pay almost anything for a tire just to get going. BTW the second worst time has to be at the RV dealer.
If your have a road service provider the tire does not necessarily need to be mounted
If you tell the road service provider you need a tire mounted and installed they should be able to send the appropriate people (you pay for the mounting) you may wait longer in a remote area but the appropriate help can be dispatched. For peace of mind also carry a bag of balancing beads/powder with you in case the serviceman does not have one or quotes an outrageous price for the bag.