Hallo!
Make a lot of holes, round or square , in the wing!
When it comes to sheeting a wing ..nothing comes close to using polyurethan glue. this glue is spread out real thin on the taped-together balsa sheets and water is sprayed on and then everything is clamped together real tight between the left over foamcore parts and some thick, 7,5-10cm (3-4 inches) board.
Forget about using contact glue!! Its more difficult to use and heavier!!!
Epoxy is also heavier so do not use it!
Use Ca glue as much as possible, except on foam I use "Flash" CA glue from Nortwest Distributors in Washington (state).

Best of luck!
Jan K
Sweden