This is my preferred method.

I use polyurethane glue, either Pro Bond, or Gorilla available at just about any home building supply store.

There is no need to edge glue the balsa sheets together. Make sure there are no large gaps when you place the sheets edges together. Place the sheets together and tape them so that they will not separate The taped side of the sheets will be the outer surface of the sheeting.

With the polyurethane glue, smear a thin film on the wing cores with either a playing card, or a foam brush. In a low humidity environment it may be beneficial to apply a very light mist of water to the side of the sheeting that will be contacting the foam. In southeast Texas this is not needed. With the core in it's associated shuck, place the wing sheeting on the core that you just applied the glue to. If you get some practice you can do both sides at once, but for your first time I would just do one side at a time. The core and shuck must be on a flat surface and the core must be placed squarely in the shuck. I usually place a cut piece of 3/4" ply on top of the shuck and weigh it down with bricks. Let it sit overnight. When you remove it the next day you will find that some of the glue has foamed into the joints of the wing sheeting. The excess glue will sand off easily and the joint will be almost invisible.

Repeat for the other side. Trim the sheeting off, add leading, trailing edges, and tips.

You will find that the polyurethane glue is much like epoxy to work with, but is lots cheaper and IMO gives a superior bond as it foams into the foam structure.

Vince