I have had two flats in my 30 plus years of motorhome driving. Both were inside duals and that motorhome had a spare tire on the back wall. Of course you can drive on the three rear tires to get to a safe place to park. This is what I did both times. As for new tires after flats, I bought new steer axles tires. I put the outside duals on the inside and the old steers on the outside dual. The way it timed out for me, each flat was on a tire around 5 years old.
2018 Hurricane 29M
CHF, Saf-T-Plus, SumoSprings