Bigger Class A's do not come with a spare for a reason...they're heavy and big.
We used our 40' motorhome for full-timing and constant traveling for 8 years. We also drove to Alaska. However, we didn't do that on older tires. Every morning when driving for the 8 years we'd check the air pressure in the tires. (We also used tire pressure monitors on the motorhome and the towed Jeep). We inspected them constantly. Yes, you could run over a nail or spike but the chances are low. Before our Alaska trip we bought all new tires - in Oregon (no sales tax). :) They were 5 years old and still looked good but they've traveled many miles and had many miles ahead of them for Alaska.
Our thinking was that if you take care of your tires and replace by age, not looks, before they look like they need replacing you have an excellent chance of not needing tire replacing on the road. In fact, we've been driving 60 years and never needed tire replacement on the road on any of our vehicles.