Welcome to the Forum.
Not sure what you are looking to hear, but if the camper was built in late Feb. The dealer got it probably in late March (maybe later with Covid). Many plants closed for a while. When it got to the dealer it was probably inspected by a mechanic. (If it was not raining he would not see a drip. Who knows if a salesman has been in it for the last couple months.
With many campers on the lot I am not at all surprised that they did not catch a small leak / drip. You apparently did not catch it on your PDI either.
No I am not defending your dealer I am just not surprised at all.
As far as to Forest Rivers warranties, the dealer is usually the big hang up. Not sure how they will take to your repair though.