First barrage with the dealer

I'd use the internet to find a couple other dealers with the same model, email them with a nice low out-the-door offer you'd be willing to pay them, and see what responses you get back. What they say will tell you how good or bad a price this first dealer is offering, relative to competition.

This is the only way to get an idea what that trailer is selling for.
Doesn't matter what profit he says they're making(you believe him?) and I have never worried about what someones profit is whether cars or trailers. I get the best price I can get "out the door". Let them fill in the blanks however they want.