Hi,
I'll give you some info to think on as you sort through this. I'll echo to be honest in your sale. If someone asks about the dings, explain it to them, straight up. Trying to hide something sets yourself up for what else is he not telling us.
That said, if you go down the get it fixed path, this can cost an amount of money. I am somewhat of a retired camper restoration hobbistet/extremist... I am on my 10th camper water damage restoration now and I deal with taking off and putting on aluminum siding without issue. I can even show you have to do it.
The siding will come off starting at the bottom. Then you work your way up. The corner molding needs to come off in order to do this. As far as the factory seal, you can restore that even better than factory if wanted. In the end, this will come down to the "labor" cost rate plus the materials along with material mark up.
Using your picture,

If the very top panel with the yellow clearance lights is not damaged, this repair will be less. If that panel can stay in place, then they do not have to deal with the roof seam along the front. The comments about having to replace the whole roof due to dealing with that seam are not accurate. You can lift that seam, not damage the roof or restore any small damage if there is any, BUT that roof seam will take time to deal with it. It can be more than taking the entire front siding below it off.
I would estimate it could take 2 techs 8 to 12 hours (16 to 24 hours) to take the old siding off, the old corner moldings off, not the top panel, clean up the corners & roof area, staple on the new siding, install new corners with new sealing tape, new Dicor on roof areas and apply new decals. I say 2 techs as most shops do this in 2's. I myself would do it with only me, but I have done it enough to know how.
Add another 6 hours if they have to deal with the top panel off and back on.
You are now up to 16 to 24 hours + 6 hours or 22 hours to 30 hours of charged labor.
At $75/hour (low end) this is $75 x 22 = $1,650 to $75 x 30 = $2,250.
At $110/hour (more likely for a good shop) This is $2,420 to $3,300.
And neither of them includes the materials, including new decals with material mark up.
While that estimate may sound high for the labor, that is reality of what a good shop may charge you. It may even be more if they find water intrusion in a corner which is likely. You having it stored in a barn is a major savings to a camper. But corner water intrusion, especially the front is real. Just because you can't see it, does not mean it is not there.
If you do the labor yourself, this is a lot cheaper as long as you want to take on the project.
Offering the new buyer $500 off if they ask about it, your ahead of the game. Granted it does not look great, but for a couple starting out with as their first camper, they may get a great deal for the money and they can live with the dings.
Hope this helps
John