my regular insurance covers off highway as well.
that's why a TJ is a high risk vehicle and some insurance companies won't insure them or have stupid premiums. I tried under Canadian Direct where we have the safari and liberty and they wouldn't. they said some special class or something for the TJ and wouldn't return my calls or stalled saying they need special approval from some head office.
also if you weren't covered you wouldn't be required to have insurance when off-road.
so it comes down to individual insurance companies and their policy. my current one stated stuff about any off highway modifications, lifts, oversized tires etc. they had to be notified. I told em what I did, took a lot of pictures, showed the agent the jeep. they submitted all the stuff and then gave me insurance.
whether i would claim anything if i rolled, i don't know. but if I am injured I would. if I started a fire I would have to. if I injured someone else.. that's my main worry and why made sure they knew what I was doing and i followed the instructions for such a vehicle to a T.