Usually, when I ship to the Nationals, I use the same 4-ball box that the manufacturers use to ship to the proshop. Use the individual boxes inside the larger 4-ball box, and if you're using 2-ball totes, you should be able to squeeze them inside. I try to fit one between the boxes and one on top.
You can ship using the USBC service, or you can usually ship directly to yourself at your hotel. I ship to the hotel because I also try to bowl the BTM, and also some practice before going to the convention center. It doesn't make sense to pay the service fees they charge at the tournament if you're going to haul your equipment around town anyway.
In the past, I found FedEx Ground to be cheaper than UPS, but this year I might check out DHL Ground, if pricing is the same on the other two.
Allow for your shipment to arrive one or two days before you do, if possible. This way, if there is a problem the shipping company has time to fix it. Also, make sure you pack your bowling shoes, braces, and your drill spec sheet in your carry-on. You can always drill a ball or three at the tournament, but breaking in new shoes is nightmare.
