Do I have to take the dealer's word on the MSRP?

Roadtrek lists their MSRP on their website. But, that is a suggested selling price. You have to assume they have already added a 25% or so to the cost to give the retailer a profit. The retailer does not have to sell at that price since it is a "suggested" price.

My experience is that dealers add onto the MSRP to arrive at a new MSRP that suits them.

If you can't get it from the Manufacturer, you really don't know what you are getting.