Whenever I've moved to a new state and insured my car, they always ask how many miles I expect to drive each year and I always say 10,000, even though I have no idea because ever since the recession I work a hodgepodge of temp/under the table/whatever comes my way jobs rather than a set, M-F destination. But I understand 10,000-12,000 miles a year is considered the average American mileage, so that's what I say. That's why I don't think it much matters what you say about your camper-van mileage when you insure it. Give them some estimate that sounds right and don't offer details about how much you drive it, where you're going, etc. Be as vague as you can and get liability or at the most, comprehensive and liability. This brings up ANOTHER issue. If you finance any part of your van through a dealer, you will be forced to get full coverage $$$. For me, one of the compelling reasons to be a vandweller is to save money. When you compare the cost of rent and utilities to the extra $$$ for full coverage, the latter is still a better deal and it only lasts until you pay off the loan (which shouldn't take very long if you have an income and aren't paying rent).
Also, for anyone of a certain age (ahem) with a good driving record, liability insurance isn't that much for a modest vehicle. I currently pay less than $450/year for a 2000 Toyota, liability only. If you're younger and/or have some boo-boos on your record, or have a high value vehicle, of course you're going to pay higher rates. That's what the insurance industry is about: risk, or more accurately, avoidance of risk. And they aren't about to take any risks without getting paid for it.
