On a related note, I would keep in mind that a lot of potential buyers will have dealt with at least a few folks in your position that have liens, owe more that what the unit is REALLY worth, and have wasted the potential buyer's time. I got to the point, while buying my last two used class A rigs, that I would cut to the chase real fast when talking to a private owner. I knew what a fair price range was, and that most will start out asking for more than that amount. Within the first couple minutes of talking to a seller, I would ask how flexible they are on their asking price? I lost track of how many folks were ask crazy amounts, sometimes well above dealer asking prices, and answered, "well, I really can't negotiate, that figure is my loan balance".
There are many sellers that don't seem to comprehend that what they owe on a rig has less than zero to do with what it's worth, and they are either going to have to ride it out until they are right side up enough to sell it, or pony up the cash to get themselves out of the hole they are in. Not suggesting the seller is in this situation at all, but if you shop long enough for used motorhomes, you tend to cringe when a private seller says, "well, there is a lien, but it's no problem" For a lot of sellers it's actually a huge problem.