As Andy said, soaking the chips should make them last longer.
But most recipes that I've seen for smoking only call for two or three hours worth of smoke. That should give you that pink smoke ring that you are looking for. I've heard that more smoke than that can give you a bitter tasting product. All that being said, I've never used a gas smoker before but I can't imagine the process being much different than charcoal.
"You wouldn't know a diamond if you held it in your hand. The things you think are precious I can't understand" STEELY DAN.