Asking for a whole new RV is, quite frankly, unreasonable. Even if lemon law applied to RVs, it wouldn't apply on the first occurrence of a problem. Needs to have three unsuccessful attempts to repair before it's declared a lemon.
You signed a contract that undoubtedly has language in it that gives the dealer and manufacturer the opportunity to remedy the issue through repair. They are never going to give you a new unit.
Maybe you should have demanded your money back. Now your only choice is to tuck your tail between your legs, take your hat in hand, and apologize to the dealer.