Confirm what I'm about to do is right ...

Gas filler tube on my Swinger goes through the body from outside with foam gasket behind the flanged end, then screwed to the body - correct ?. The reason I'm asking - when installed this way, the gas cap I bought which is supposed to fit Swingers - stands a half inch off the fender, it'd fit right if the flange for the tube were behind the sheet metal - I nust have the wrong cap (had it painted and everything - sucks)