Ave - you'd have to 'remote' the vent at a level above the top of the tank, which would kinda require making a new hole in the body at that level .... not sure why you'd be smelling fumes from the cap vent, it's only a pin hole and should be drawing air in as fuel level goes down, not 'venting' fumes out - I'd suspect that the rubber vent connection inside the cab is old cracked rubber, or as Tony says, the joints/clamps are loose or you have a pin hole weeping under the tank
Bill
