In addition to the regular liability and collision/comprehensive that most vehicles have, a fulltimer is wise to have an "umbrella" liability policy to provide coverage for anything that he may be liable for outside of an accident involving the RV itself. If you have homeowner coverage on a dwelling, this is normally part of the package, but a fulltimer needs to get it some other way. You can risk living what it - most apartment renters do - but it is a risk.
Babylunatic's $500-$2000 is about as close an estimate as can be made without lots of details. And that doesn't include the liability umbrella policy either. To add a data point, my coach insurance costs a bit under $900/year and its market value (a major factor in collision and comprehensive cost) is around $100k. That's for a coach insured in Florida, which is neither the cheapest nor the most expensive stae to insure in.