I was over at the escapees website. They say you can use their addresses for your own address on your license, registration & insurance.
I know States vary widely. In New Jersey, they want an actual dwelling place with an actual street address.
As far as legality, it appears that you must register your vehicle as an RV in order to be legal. This requires running water, built in stove & a built in refrigerator, as well as a black water & grey water system.
I hear/see that many are not doing that. Currently, I'm not doing that. Insuring your vehicle as a regular vehicle can result in your policy being cancelled if anything happens.