First try tightening the hose clamps and/or replacing the rubber tubing for the filler neck and vent tube.
My cab absolutely reeked after every fill up. I put in new 1/2" vent tubing, tightened all the clamps and it cleared right up, for about $1.50.
You also may be able to see fuel dribbling down the side of the fill neck behind the seat, if the neck is the problem. I had a puddle on the floor and running board which clued me in on where to look.
