I agree with everyone that prep fees are stupid and I also agree that it doesn't matter at the same time. If the total price is X and that price is acceptable to me, what do I care?
We'll that now gives me insight into this dealers business practices and it concerns me that I will drive 100+ miles to get the shaft in some way at the time of sale. If the dealer were down the street it would less concerning.
Anyway, I offered to split the cost with them and have not heard back. So if I want the trailer, my only choice is to proactively follow up with them, which weakens my position further.