I have heard of both parties going to the bank at the same time with the money.  The buyer hands the bank the balance of the lien and the seller takes the rest of the cash.  The bank then hands over the title.  Now I don't know how it works if the lien isn't with a local bank. 

My in-laws sold a car with a lien to other in-laws and the buyers just gave the sellers a check to send to the bank and then a week or so later they had the title.  But that was "family" and nobody was going to screw anybody.

What I might suggest is to tell the seller you want the camper and you will pay $X.xx.  Maybe the seller has the savings to get the title and you can come with the cash when he has the title in hand.