1989E150

I have a 1989 E150, with the 4.9 straight 6. After van is warmed up I am smelling a fuel odor from the front, especially in hot humid conditions. No fuel leaks, filter was changed. . I have locking fuel caps on both tanks, Duralast part number 5991.. I found a vacuum hose, coming off the top of the throttle body, but no vacuum leak was observed when I removed the plug that was in the hose when I got it. I also, found a 3/8" line on top of frame rail with no hose going to it, and a hose at the charcoal canister was very rotten. Questions here are, would the locking gas caps cause this? I don't know where the hose coming off the throttle body is going, perhaps it goes to that line on the frame rail? And how do I remove the shield, that is covering the canister??Underhood diagram isn't much help as I have hard time seeing small print