I've found the 'water with a drop of soap method' to work very well. The idea is to take a squirt bottle and fill it with water and a drop of soap. wet the back of the decal and apply it to the airplane. The wetness allows you to manipulate the decal until you get it just right... then carefully squeegee the water and bubbles out. Allow it to sit until dry, and you'll have decals right where you want them and impossible to remove.