depends on the plane but before I cover most of them I like to build a small frame onto the plane about 1/8 high that fits on the inside of the canopy. I use thin balsa for this, wet it with water and ammonia and it bends very well. I cover the plane and then trim around the frame. I paint a trim on the inside of the canopy to hide the frame then I use canopy glue like the 560 huck mentioned. Often the frame isn't needed, the canopy glues work very well on there own, just glue the canopy onto the covered plane and hold it down with masking tape and let sit until it sets up.