If the unit you're buying is from a major manufacturer, anda local dealership refuses to do warranty work... Call that company and ccomplain . There's nothing a company hates more than bad business from one of their representatives. They're trying to keep you in their family of RV's, a company like Keystone or Forest River would come down hard on one of their dealers refusing service to their customer.
I don't doubt it happens often, but I've talked to my local dealers, and they've told me that have no problem whatsoever getting me in for service. I'm traveling 120 miles one way this week to get my new TT.