West to east routes
Boy are you going to have fun flying this route in March!! Check all the weather services you can find, like wx channel, wx undergound, aopa wx, etc. and pick a route with the best chances.
Consider the following routes:
Northern route - Seattle over Cascade passes east to Missoula, Billings, Rapid City, then direct southeast to your destination. This was beautiful last August but I would not expect this one to work well in March.
Middle route - Columbia river gourge down to Boise area, Logan, Cheyenne, then direct southeast to your destination. We travel this route often in summer and is really doable in a GA airplane without needing oxygen.
South route - south along Cascades crossing where weather permits, then to Winnemucca, St. George Utah, then Farmington, Alburquerque, then direct southeast to your destination.
My assumption is that once you clear the Rocky Mountains you can pick the best route for weather and make it SE.
Check Airnav for fuel prices and good luck. Let us know how it goes.