I ended up getting an xBox analog joystick rather than a psp. I'm thinking that if I mount it snug with an o-ring and grease we will get good life out of it. The buttons should be pretty easy to weatherproof comparatively.
Parts arrive next week I think and I'll be working on a remote prototype. I didn't get a GPS module or magnetometer (compass) yet, but I am considering both. An external GPS module will run about $80 and the compass about $50. The compass is great because it is a highly accurate direction circuit regardless of speed. It would be sensitive to the moving of the bars though...