Congrats on the trailer! On the point of your post, many just have to understand that large "markups" are the norm on such a large purchase of this type. I mean look at the $7000-$10000 off ad's on TV for trucks during truck month or whatever the marketing gimmick is every quarter.
These forums are full of people that negotiated 25%-30% off New trailers. Even have a few that if they are honest will tell you they traded in their trailer for about 60% of what they later saw it listed for on that dealer website.
So know that listed or MSRP is a number that no one expects anyone to pay for NEW or USED trailers. Many private owners are having a hard time coming to grips that they are upside down in a 15 year loan of their trailer and it's worth about half what they owe on it. Some decide that they want a new trailer bad enough to trade it in, take the loss and move on. The smart ones list it, listen to offers for a while and sell it for somewhere between what the dealer offered and low retail.