Its recommended ST tires be changed every 3-5 years so you got your monies worth and then some out of them.
Of course many RV trailer owners time out before the tires get many miles and dry rot sets in.
Good point on knowing how to change a flat tire while on the road. I'm on the old mother road (US-66) daily in a 65 mile stretch. I probably average twice a month stopping and helping someone with some type of tire issue on some type of trailer. And most of them are not equipped to do so.