First the obvious - NEVER EVER pay for something this expensive in full until your have seen it complete and can take immediate possession.
You didn't state how the damage occurred - specifically did the boat ship damaged?, did the transported damage it? did the dealer damage it in his shop?
If it shipped damaged, its a Bennington warranty issue.
If it arrived damaged, its a transport claim. Dealer and Bennington need to be involved.
If dealer damaged it, he has stupid operator insurance that will cover the claim. Since you paid way in advance, did you insure the boat immediately? Hopefully. If so and its a dealer issue, call your insurance company, report the damage, file a claim and pay the deductible. They will replace the pontoon and subrogate the claim to the dealers insurance and you will get your deductible back. Sometime just the threat of this will make it happen.
Regarding my opening comment, a few years ago a friend bought a new Ford F450 pickup for his house building business. They called him when it arrived from factory and when he went to pick it up it was leaking oil. He looked at the salesman as he turned away and said "call me when the leak is fixed and we'll sign paperwork" and walked away. They diagnosed the problem, had parts overnighted from Dearborn, and had it repaired in 48hours. Why? They hadn't been paid!!!.