what is reasonable profit for the dealer

Unlike buying a car or truck there is no easy way to find out the invoice price (the price the dealer paid for the unit). The Net is full of sites where you can easily find out what a dealer is paying for a car or truck. The rule of thumb when buying cars or trucks is to always negotiate UP from invoice and not DOWN from MSRP. When I buy a car or truck I come armed with that information. If a dealer claims my numbers are incorrect I ask to see the actual invoice. If the dealer balks at showing me the true invoice I walk. Most reputable dealers will show you the true invoice. The window sticker (they do have them) for RVs varies from dealer to dealer. It is my opinion that the dealers tell the manufacturer what to put on that sticker. The Magneson-Moss Act regulates the window sticker for cars and trucks. Any of those vehicles will have the same price anywhere. This is not true for recreational vehicles.
A few years ago there was a RV dealer releasing the invoice information for publication. I do not remember the exact details but he was forced to stop by the manufacturer(s).