Not a lawyer but it seems to me that you ordered a very specific product, it appears you got that order in writing,, The dealer is now trying to SWITCH you to something you did not order.
As I understand it he can get in SERIOUS trouble if he does that. The price was finalized when you signed, so was the color and the options. You get what you signed for or you get a refund WITH INTEREST and perhaps a bonus if you apply it to a different RV.
Though personally.. I'd consider a different dealer.
If the dealer gives you any heat, A contact list...
Department of motor vehicles (Dealers license is in jepordy)
Better business/Chamber of Commerence
News media (Any action line, including FMCA & Good Sam)
The manufacturer (might be interested in why you are buying a Tiffin instead of what they make).
Lawyer (hey, if you got to you got to).
Basically make noise.
Home is where I park it!