I don't know how much you are paying them for this RV, but I'm sure they should be able to replace the coroplast and still make a lot of money; it is not that expensive and a few hours labor. Stick to your guns; "you fix it, I'll buy it".
You are probably going to have this RV for a long time and this will haunt you. Any tape will probably have to be replaced periodically; however, I have no experience with tape; I refuse to cut into mine or let any shop do it.
And, yes, after they drill out the power nails have them reinstall with #10 x 3/4" Tek screws and fender washers; will save them time and make your life easier down the road. Use the same holes the power nails came out of. Throw them a bone, tell them you will buy the screws and washers.
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Scott & Alta
2017 Montana 3160RL, Legacy, Onan 5.5Kw, Solar
2022 F-450 Lariat Ultimate