I hate to tell you that the spread between true wholesale cost and MSRP may not be the same at every manufacturer. Who knows if actual cost is the same between dealerships either. A manufacturer may give the selling dealer a cash discount or even a volume purchase discount. Or a dealership may be given a discount if they drop a competitive brand.
You've just got to shop around--to dealerships within reasonable proximity to where you live--if you intend to use their service department. And you often cannot be hung on one brand/model of RV. If a brand is unavailable in your retail market, go for a comparable brand/model.
After all, the RV business is not the car business. A medium size car dealer sells 50 units a month. A medium size RV dealer might not sell 50 units a year. And both have comparable expenses on facilities and personnel. There's no $100 deals going on in the RV world if the dealer's going to be around very long.
Prices are all relative--between dealerships for comparable models.