Another similar case to this point; was soon after I bought my new Ram. I had just recently replaced both summer & winter tires on my previous truck and the Ram tires were junk, so I kept the previous sets of tires and the dealer agreed to perform the tire/rim shuffle.
One fine day that summer, I picked up a roofing nail in one of my Michelin Defenders, and too close to the tread block. The tire was garbage and couldn't be repaired.
So, being the frugal Costco member that I am, I ordered a replacement at Costco to match the other 3 tires. It was the best price and had a road hazard guarantee that I couldn't find anywhere.
Doesn't the mechanic call me to advise that my selected tire was just slightly below the specified tire load rating on the doorjamb sticker for my truck and that Costco would not be able to install that tire under any circumstances? It didn't matter about the other 3 tires on the truck.
I didn't get nasty with the employee doing their job but wasn't too impressed. The bottom line is; they were protecting Costco's liability, which is I believe the same story here.
Had there been death and dismemberment associated with this silliness, as daft as the owner might be, I believe that a large amount of the responsibility would likely have fallen on the camper installation company.
YMMV