Ok - finally got a response from the factory.
My question was ...
"We have a 2016 Vengeance 25V with the deck/patio kit. Is the ramp water proof? I'm not talking about days and days of rain or using it like a boat ramp but if it gets rained on while camping or loading/unloading, do we have to worry about it for the long term?"
Their response ...
"These ramp doors are not 100% water proof. You can lower and load in the rain, and if you have the patio system up and it starts to rain, then you better close it soon. If it gets wet, you are OK. But I would not leave it open an extended amount of time. Water will finally seep into the inside of the door, and if enough water gets in, then your door will start to swell, and have issues. I did however like your boat ramp scenario… That was good."
And to think, when I asked the dealer they told me the rain won't be a problem ... good thing I don't believe most of what the dealer says!
So, what this says to me is I need to seal the door better (caulking or DYI bedliner, etc) so I don't have to worry about this, as much, down the road (as in years not mileage).
2013 GMC Sierra 2500DH CC, 4x4, D/A
2016 Forest River Vengeance 25V TT/TH