BATF disagrees with you. You can be a resident of more than one state for the purpose of purchasing firearms. I own property in Arizona and live there for 2 - 3 months out of the year. BATF says I can legally purchase handguns in Arizona when I am actually living there. I was also told that quick trips over the border do not qualify.
Here is what they say on their web site. http://www.atf.gov/firearms/faq/faq2.htm#b13
(B13) May a person who resides in one state and owns property in another state purchase a handgun in either state? [Back]
If a person maintains a home in 2 states and resides in both states for certain periods of the year, he or she may, during the period of time the person actually resides in a particular state, purchase a handgun in that state. But simply owning property in another state does not qualify the person to purchase a handgun in that state.
How do you figure BATF disagrees with me? BATF says you can only purchase a handgun in the state you are actually residing in. That's what I said.