You won't find insurance for tires. You will find road side assistance which is not insurance. In the event of a blowout they will dispatch someone to change your tire, if you don't have one they will bring one. Road side assistance will pay for the service call, but you pay for the tire. There is no such thing as tire insurance as far as I know. But RSA and Insurance are 2 very different things.
The 2 main RSA for RV's is Coachnet and Good Sam. I prefer Coachnet but many swear by Good Sam. I am sure you'd be fine with either.