Karla,
I use the safety pins that are curved made special for quilt basting. I use them for hand and machine quilting. I used to hand bast with thread and a millerners needle. Getting all of the basting thread out was a pain. I try to place them about 4 inches apart all over the quilt. I open a bunch of them at a time and put them in the sandwhich and then open another batch. I have used straight pins but I am on blood thinners and bleed profusely if i stick myself.
There are spray adhesives that work fairly well. Just be sure to use them in a well ventelated area. I have used them on smaller projects.
mpspeedy
Manchester, MD