Just install laminated insert decals on top of cleared and cured playfield and then buy a Makrolon (polycarbonate) playfield protector to go over that. Now you can have a perfect ball surface without fuss and concern about inserts popping up. This is my plan for F-14 Tomcat which is notorious for that problem. Playfield will last forever. No need to worry about building up low spots or multiple coats. I figure two coats is plenty. Use a fine bristle paint brush. Way simpler than all this spraying and toxic auto clearing. 

http://playfield-protectors.com/