We purchased our Class C MH while in NJ. We live in GA. We did no pre-planning as we did not expect to buy the Motorhome while in NJ. We had been looking for a long time, but we went to NJ for a wedding and ended up buying a new MH while we were there.
We financed the Motorhome. The dealer collected sales tax and then gave us a check made out to our County's tax collector to give them when we registered it. (in our county, the Tax Commissioner does both Property Tax collection and Vehicle Registration) He told us if we had paid cash, they wouldn't have charged us sales tax and that we would just settle up with GA when we went to register it. In NJ, they do not tax document and licensing fees, however in GA, they do so we had to pay another $18 or so when we registered the MH in GA.
The nearest Jayco Dealer to us is about 2 hours away in St. Augustine, FL. When we contacted them about warranty work, the service rep did not say they wouldn't do it, but he did say they were really busy and it would be a few weeks before they could look at it. I took that to mean they didn't want to do it. We contacted the next local dealership about 3.5 hours away in North Charleston, SC. They were great and handle our warranty service promptly. It stunk having to drive that far, but Charleston is a great city so we made a day of it when we dropped it off and picked it up.
I have heard plenty of folks say they have had issues with their local dealer not wanting to do warranty work on a RV bought elsewhere. That was not the case for us fortunately. The FL dealership didn't flat our refuse.
If you know what manufacturer you want to buy from, it might be worth taking the quote you get out of state to your local dealer and see if they will match it or come close. If the difference isn't much more than gas money/travel costs to pick up out of state, it would probably be worth it to buy locally. If they can't, at least find out if they would honor warranty work on it.
-Michael