Question about out of state purchases.

I wanted to know if it is possible for my father, a NYC resident, to purchase a long gun in PA?

He has property in PA but his actual residence is in NYC. I realize long guns are legal to buy out of state but I wanted to know how likely it is an FFL would be to allow him to purchase from them? Furthermore is there anything he could have to help make the transaction more or less easier (such as proof of ownership of property in PA?).