You probably need to prove residence with documents the state accepts. A lease with a street address, a utility bill in your name for a place with a street address, a copy of a rental agreement, a rent receipt. You can wiggle with getting the place you are staying to agree to a lease, but not as a camp ground, but an RV park, or other approved rental site.
When I lived in Oregon I proved my address with a rental agreement, and a permanent mail box, so the state could reach me. Here in Utah I have a physical address, I own, but get my mail at a Post Office. It took a little persuading on my part, but it now works fine. Talk with a supervisor, be honest and see what happens. They are more flexible than the rules might say.