Taxes when buying a pop up camper from out of state

Here in PA, if you purchase out of state, they ask to see your bill of sale and if you paid sales tax. As mentioned above, you get "credit" for what you already paid.

If you provide your out of state ID at the time of sale, you can claim exempt from sales tax and then you will pay your local state's full sales tax when you complete the title/trailer registration stuff.

Not everyone will cooperate with the second option, but many will, in my experience.

YMMV.