I'm hardly an authority, but I think a U-Haul
in average condition here in the Midwest goes for $4500, give or take. Prices may have gone up a bit with the whole Coronavirus thing, and people wanting to do self-contained getaways.
Prices are substantially higher on the coasts.
An informed buyer will be on the lookout for  soft/punky/damp spots in the flooring--just inside the door, or underneath the seats. Rear side windows
have a strong tendency to leak, and it can run down the sidewalls and underneath the seat platforms.
 Missing "elevator bolts" that hold the body to the frame. (about a third of them were missing on our CT when we bought it)
 Rusted-through corners on the tubular frame--maybe most likely right behind the rear wheels. Frames can get expensive to repair.
 Clear title
. If people live in a state with a fussy DMV, this can be a deal-killer.
Good news, though--these are really popular little campers. If it's in overall good, sound shape, it should sell quickly.
You could join the Facebook U-Haul
camper page, and advertise it there as well......they're an active community, and someone's always looking to buy one.
Best of luck with the prep & sale,