I suggest having an EAST/WEST alternating nationals each year.

Sports/Club
15M/Standard
18M/Open
PW5/1-26

For Example, with National Contests:

In 2013 host the Sports Class at Chilhowee and the Club Class at Parawon
In 2014 host the Club Class at Chilhowee and Sports Class at Parawon

In 2013 host the Standard at Mifflin and the 15M in Uvalde
In 2014 host the 15M at Mifflin and the Standard in Uvalde

If you flip flop these 8 classes to have 4 nationals each year on the west side of the country and the other 4 nationals on the east side, this should even things out. If you divide the USA into two halves, then centrally locate the nationals in each half, then driving time should be no more than one day.