RE: Sheeting a wing
If you are using carpenters glue (alphatic or PVA), you could try the iron on method. Apply glue to the ribs and place the skin on and then remove. This will transfer some glue to the skin. Re-apply glue to the ribs and any dry spots on the skin that will contact the ribs/stringers. Let dry for about an hour. Now place the skin in position and using a covering iron, iron over the skin and ribs. The heat will reactivate the glue and give an almost instant bond. This works particularly well if there is a sub leading edge to support the front edge of the skin.