GPS module already contains some kind of procesor, which is capable of driving NIXI tube's driver. Of course it will require to integrate custom code with GPS firmware, this may be at least expensive. Otherway FPGA is really pain is the ass, in such simple project, where 8bit microcontroller will be much cheaper and easier to applicate.
@Nnanci: what are some of the modern day practical uses of nixie tubes
Before 7-segment LED displays came on the scene, Nixie tubes were the height of technology. Today, I don't know about "practical uses of Nixie tubes," I just knwo that they look really cool and retro. For example, I LOVE my nixie-tube watch from Cathode Corner
I love Nixie Tubes -- you are absolutely right that it gives the right vintage feel as an add-on to an old truck. Funny, though, when I've seen the Nixie tube watches I feel like they look very futuristic!!!