I meant taking it for a spin myself, privately....
That should be fine as a private arrangement with an RV owner. Check the insurance situation - has the owner nominated you on the policy, are you covered for third party damage? If you force land in a paddock and the subsequent fire burns down a crop or a machine shed, how do you stand?
It's no different from borrowing a certified aircraft really - just that with an Amateur Built Aircraft Acceptance or Experimental category aircraft, the insurance company might use the fact that you are 'hiring' the aircraft to weasel out of a payout. Borrowing, without payment, would be legal I think.
And if your'e going to take it for a spin, remember Vans recommends no more than 2 turns in the 6
