You're not a dealership in the business of selling RV's. This guy is looking for a warranty that even dealerships rarely offer. If he finds nothing wrong at purchase, he can buy his own aftermarket warranty, like good Sam offers. Why would you be required to provide a warranty.
I would politely tell the gentleman that coach is for sale in AS-IS condition. By the way, in most states, private party sales are always AS-IS. If he would like to bring an RV inspector with him, he's more than welcome. I wouldn't make any special offers to assist. If they find something substantially wrong, you can negotiate that into the price.
Personally, anyone asking for such an open ended warranty I would tell them, sorry, it's AS-IS, call me if you're interested with those conditions and be done.
