1. You probably can't know, and no way to verify.
2. Probably not much difference.
3. The dealer will make their money no matter what. You might be able to get them to knock off the fees, but they won't come down as much on the price of the vehicle. They're entitled to make a profit.
In the end, what you're after is the "out the door" number. I doesn't matter to me if they charge $1000 for the trailer and $19,000 in fees, or $19,000 for the trailer and $1000 in fees. In the end, it is still $20k. If you're happy with the that number, then buy it. If not, haggle more or walk away.