From the OP's first post, it sounds like he "paid for the trailer a couple weeks ago but hasn't yet picked it up"....
If that's the situation, then the trailer is "HIS" and the dealer is "NO LONGER MOTIVATED TO OBTAIN HIS SIGNATURE ON THE BILL OF SALE"....
In other words, as soon as he signed that document, the dealership had their money and the dealer's priority shifted from "obtain the signature" to "got the signature" and his priority moved away from this buyer to obtain signatures from other potential buyers...
It sucks to become a "second rate customer" but the reality is, that's the "circular file you now find yourself in"....
As for contacting Keystone, you can do it at the "Customer Service" tab on their website:
https://www.keystonerv.com/customer-service
You can "fill out the web form and wait for a reply" or you can "call them at (866) 425-4369 during normal business hours (CST)."
Keystone has a "customer warranty repayment program" and they MIGHT (note maybe) pay you to do the work yourself rather than dragging your trailer to the dealership for warranty repairs and having it "held hostage for weeks and weeks".... Ask about that program if you call Keystone.
Now, as a "final comment" If I were you, I'd use this as a "learning experience with that dealership" and I'd cease to spend my money with people who don't/won't take care of me as a "valued customer"..... Next time you start looking for a nicer, bigger, better trailer, I'd "drive right on by that dealership" !!!!! YMMV