[FWB]

well the tank is vented via your cap, now you just have to get it away from the passenger compartment. is the smell a problem only when in a garage?
i have considered a small charcoal canister in the wheelhouse with the vent hose in it. every car on the road has a charcoal canister the trick is to find the one that plays nicely with the stallion. there is room for one in the wheelhouse and there is room under the car between passenger compartment and trunk bulkhead.
i do have a question though, if you have the stallion cap assembly on the car, where is the vent? is there a hole drilled into the aluminum disc? if so somebody did this previously to get rid of the trunk smell. the caps never had a hole in them. post a pic..... if this is the case you possibly need to go back to the cap the way it was designed, with no hole and vent another way.
because if its just a hole in the cap under certain driving conditions fuel can squirt out, there isn't a baffle to stop slosh in the cap.