I used to work for an insurance agency; I know a little about a little.
If you get the vehicle insured as an RV, the ins. co. is going to assume low mileage. They will probably note the mileage, and if you have an accident, they will check the mileage again. If they find that you've traveled "an excessive number" of miles in a year, they may object to insuring as an 'occasional' vehicle, and raise the premium. Insurance is all about odds: Every mile you drive increases the chance that you'll hit them with a claim. If you falsify information, they may not pay a claim, and if they do pay the claim, they may cancel your insurance; and if they cancel your insurance, every other insurance agency/company will find out about it, because they will check.
If you buy a cargo van and install a bunch of goodies in it, AND want all those things insured as part of the van, it may increase the premium cost considerably. Balance the replacement cost against the possible/probable premium increase.
Another issue with ins. co's is that they keep track of every question you ask them, and that question can raise your premium, even if you don't follow through with what you were asking about. For instance, if you have a home, you have homeowners/liability insurance. When you bought that insurance, they probably asked (very casually) if you had a dog and maybe you told them that you had a Pug or Standard Poodle (low-bite breeds). If you called them tomorrow and asked if owning a pit-type breed, a wolf-hybrid, or a Rottweiler (high-bite breeds) would increase your insurance premium, they would probably tell you: 1) Yes, it would increase, or 2) No, it wouldn't because they would cancel your policy. And the next time your policy is renewed, the premium would probably have gone up, even if you didn't get the dog. They seem to assume that you would get the dog and not tell them.
Always remember this Number One Rule: Insurance Companies are in the Premium-Collecting Business, NOT the Claim-Paying Business.