I have mine with Progressive. Have not had a claim so cannot give first hand info on how they handle them but I have not read any negative reports on their service. They were very easy to deal with and had the best rates when I signed up. I have both my trailer and motorcycle with them. Here is their web site. You can get quotes on line and even sign up on line. http://www.progressive.com/
Another company is Formost. Also, Campers World, Good Sam and other Afinity owned groups have good rates and service. You might try a Google search with "RV Insurance" to find others.
Hope this helps.