Just get yourself the glue sticks, and when something is coming loose, just rub the stick a little under the applique, don't have to use a lot, press it down, and you are good to go. Be sure and don't iron on all of your appliques at once. Iron some on, then applique them and iron on more. Do the ones that have to overlap together. I always position my applique pieces, and before I iron them on, I always put a tiny rub of the glue stick under each one, just to tack it down, like a bit of a stitch would. If you iron everything on at once, while you are stitching and moving your quilt around, they will tend to come loose. Hope that helps.
I like Heat n Bond the best, much better than Wonder Under.
Don't use basting spray. You will have a complete mess all over your project.