Back in the 60's the standard industrial markup was 2.5. that means something costing a dealer 100 dollars carried an MSRP of 250. But some stores only marked up 2.0 so they sold it at 200. You saved 50 bucks.
Today in many cases the markups on many products (NOTE: I am not specifically speaking of RV's but am specifically of other things) 3,4,5, 50 or more.
So a "Dealer" who marks sometown below MSRP may have negotiated a better price from his/her supplier or may just be counting on volume to make up for the loss of per-item profit.
ALso on RV's you have "After sale" sales and service.. Very high profit stuff.