We just bought a used RV, so can talk a bit about our experience.
Nada is a shot in the dark, and tends to be low for desirable makes and models/configurations of particular RV's.
We found used pricing with private sellers was all over the place. Many of them were so financed-to-the-gills in stuff that there was no wiggle-room on pricing. Most of those units are still for sale.
We found our used RV at a dealer. With dealer pricing, keep the following in mind:
More than half the battle for a dealer is to find a buyer that is willing to buy NOW, and has the adequate means to do so, and knows exactly the rig they're buying. If you're paying in cash, it's available and ready to transfer. If you're financing, you're already pre-qualified for the amount you anticipate to spend. Having a buyer equipped and ready is GOLDEN.
The other part of the battle is closing the delta between asking and offer pricing. It's easier to close a 10-15% delta than it is a 20-25-30% delta, and if it's that large, one side of the deal isn't being competitive for some reason or another. Either the buyer is being unrealistic or the seller reasonably thinks there's a buyer to be had at the higher price, and that's fine. Nothing personal...dealer isn't a ripoff or a bunch of jerks (unless they treat you that way), you just aren't the buyer they're looking for, for that particular RV.
To close the delta, you need to know and stand firm on general market pricing by looking at everything that comes up for sale. Use that data as a baseline from which to work backwards. Be able to negotiate using things about the RV itself - condition, maintenance needs as a concession, or exact-models for sale for cheaper, and your ability and willingness to close the deal on that day can have some real swing.
Here's the thing: A dealer doesn't want to give you their best number for a used rig on a sheet of paper so you can take it somewhere else to have another dealer try to beat it and have their chance at you, presumably on a different used rig. Good dealers (the ones that sell RV's, not just sit on them) will reach deep if they believe there's an earnest buyer that will close the deal.
Cross-shopping is great with new rigs all equipped the same and based on a set MSRP baseline, but doing that used, you could be leaving your best deal on the table. So sit down and negotiate versus "shop", get into a deal sheet, be ready to buy. If it's not right, it's not right, say thanks, shake hands, and part ways. (And NO callback games, or walking out in a huff...make it clear that you have given your best offer, all possibilities should have been exhausted...just like THEIR deals, yours is also one-time, only).
We used the same strategy to buy cars as we did our first RV a month ago and it was fine. Candid negotiations, we were equipped and willing to buy, and they took the opportunity to move a used RV by working with us on price and concessions. But they also weren't asking fake prices, it was within market range.