We had National Interstate (since 2001) until last year, when they "got out of" RV Insurance.
They "assigned" us Liberty Mutual. Our agent called...they carry both Liberty Mutual and Progressive, said that for our needs, Progressive is better...so we went with Progressive. 1 year now, no claims, have no idea what any problems might be...and hope I don't find out.
Some years ago, Camping World was pushing insurance for RVs. Investigating, I found they were using GMAC (now called "ALLY"...internet only) and the premium quote was almost double what I was paying for National Interstate. Guess what.
Look around. Quite a few RV insurance companies and plans out there. G'luck !