Need some advice on gas tank!

[Bean Counter]

Has anyone used the poly replacement tank on their truck? I'm in the test-fitting stage and I don't like where the filler neck is positioned (see the pic). I had planned on using an in-bed filler neck. As the filler tube is currently positioned, it goes almost directly through the sill which I've already notched. Was curious if anyone else had run into this problem and what they did. Did you just "go with it" or other?

I would really like to relocate the filler neck just slightly forward but don't know how to seal the current opening and safely make a new one. Any suggestions - or laughs - would be appreciated!

Thanks,
David