I am extending the wing tanks on my LNC2 - Wankle 13B which are already built and will do it this way.

Cut a 8" X14" hole in the top of the wing. Mount the fuel cap in the cutout piece.

Extend the aileron pushrod actuator tube through the next section of the wing and seal the new section for fuel.

Saw cut some openings in the vent line.

Hole saw 3 fuel transfer holes in the existing rib and seal raw edges.

Glass in 1" flanges on the inside of the 8"x14" hole.

Epoxy in the 8"X14" cutout with the fuel fill cap in it and lay up 3 bid on top to maintain the wing structure.

You can seal the existing fuel cap location by flanging the hole on the inside and epoxy on a patch as described for the 8"X14" above.

I am using the header tank area for my radiator and besides I did not like a gas tank in my lap flying a J3 57 years ago and I still don't like it

Hank Huddleston.