On the question of the gas cap, the spring/tensioner is broken. It's been discussed before on this forum. Only fix is to remove (remove pin to get at broken spring).
I opted to replace with a black billet with a locking door; Scored a used one for 20 bucks.
"Never argue with an idiot; they'll only drag you down to their level, then beat you with experience"
2007 F150 STX Supercab (4.6 2V V8), Edge tuner, factory navigation, Mark VIII electric fan conversion with flex-o-lite controller.