How do you move a motorhome purchased from another state

You drive it.

Sorry, couldn't resist.

Get your own insurance. Don't depend upon someone else's insurance.

Then drive it home. Make sure you have a notarized bill of sale and a copy of the old registration. If the seller will leave the plates on, fine. If not don't worry. You might get stopped, but the policeman will understand your situation when you provide those documents.