Autos are different than trucks and a motorhome is going to be different from a trailer or a camper. RV dealers are selling far fewer units per month and yet need to pay the rent and meet the payroll and other fixed overhead costs and so need to make more on each one they sell.
I would also expect that the dealer going to be more flexible with an RV at the upper end of the range than an economy model where they probably make half or a third as much profit on the sale.
As with cars and trucks it is the extras where you pay the biggest markup and also where you can negotiate. With our camper I got a $800 AC unit installed and I paid $350. I got the AC at the dealer's cost and he agreed to not charge for the hour of labor to install it. Others have paid the $800 and $100 or more for the labor and been happy with the deal.
The basic rule is it never hurts to ask and there are multiple ways to save money. A lower purchase price is one, free extras are another, extras at the dealer's cost is another, and then there is getting any installations done at no charge.