Agree with so many others, no way I'd sign what he is asking for. Like already said, that amounts to a 'blank check' warranty for him.
At the same time, though, you can't be too 'hard-ball' about it, or you may end up losing a good chance to sell your RV for a good price.
I would offer this as a 'counter-offer': OK, we'll have your mechanic inspect it at your location (2 hours away). I'll bring the RV there for the inspection, provided that you (potential buyer) pay for the gas to bring it there and back, regardless whether sale is made or not.
And, I would make sure to get the gas $$ from him BEFORE his mechanic gets to see it. Maybe agree to meet him at a gas station, where he will pay for you to fill it back up with an agreed upon amount of fuel before going to your mechanic? This way, if he backs out for whatever reason after inspection, you're guaranteed that you won't be out anything but some time.
Not sure about your RV you are selling, but mine, a 2 hour trip and 2 hours back, would burn up quite a bit of fuel. I would not want to 'eat' that cost, unless I was pretty certain it was going to result in a sale.
