Not to be a spoil sport, but how would most people feel on the other side of this transaction. Some guy is asking for people to leave a non refundable deposit on a RV he does not own and has no ability to legally sell. That deposit will either need to be cash, or a check made out to either the non-owner or to someone the buyer has never laid eyes on. Not much recourse for the buyer should the whole thing be a scam.
If I was the buyer, I wouldn't offer anything other than a hearty handshake and my phone number for the owner to call when they are able to actually complete the sale.
