Even though I have never traveled out for nationals, when I went out to vegas for the TAT tournaments the past couple of years , I bought 2 of the 2 ball cases from caseclub. There is room for 2 balls + shoes and accessories in each one. What I like about those cases is they are sturdy and durable and when I fly out on Southwest, they each fall within the size and weight limits to fly free...I put as much as I can in my free carry on and I pay nothing extra for baggage...it does limit me to only 3 strike balls and a spare ball. but these I will be able to use for air travel for years to come. The company also makes a 3 ball case and a 4 ball case, but with those you'd get stuck with extra charges to fly and then they'd be quite heavy to deal with.
Brad