If it were me, I'd also fasten it from the bottom with screws w/seals for a couple reasons;
1. A screw is going to instantly reveal if there's water under there once the panel is pierced.
2. The mechanical connection of the screw is going to be many times stronger than glue from the other side as the factory described installing.
With that said, the factory can't be given a free walk on this. I'd say the defect is worth at least 10% of the camper cost. Either in a direct refund, a reduction of the loan amount or credit towards products they carry. I'd tell 'em I will deal with the problem as long as it's not water related and that I want the 10% compensation for the defective camper. I'd also tell 'em I'm returning the camper for a replacement or my money back if they don't agree to my terms.
No way would I let some 'RV Shop' attempt to 'repair' this.