Hi Mike,
Had a similar issue last year with fuel smell coming from the trunk (mine's a tr6). Turned out that the top third of the tank was begining to deteriorate, and gas was actually seeping out of some rust spots. Not sure how accessible the tank is on a spit, but this could be something you can check after you top off the tank. I ended up resealing the tank using the por-15 sealer system. However, I still get a slight fuel odor which I am troubleshooting.. probably a loose vent hose (or maybe the fill hose section has worked itself loose).
But the fact that you can smell it while driving with the top down, would seem to indicate that it is coming more towards the front of the car, in which case DrEntropy and Tom have offered some excellent suggestions above.
Good luck, Steve