I was having trouble with my Greg L. collar binding on the heads of the screws holding the mounting tabs. I didn't want to make the fiberglass any thinner by recessing them so I decided to go up instead. I Super Glued on a piece of stiff insulated wire that had a hard clear coating over the insulation and was just barely thicker than the heads of the screws protruding. It's almost unnoticeable between the collar and torso and it also provides a hard smooth surface for the collar to slide on.

Regarding drilling the bubble and bottom plate: First I marked where I wanted to drill with a marker. I then took an Exacto knife with that standard blade it comes with when you buy it. Stick the point on the marker dot you've made and start turning the knife back and forth, or you can make complete circles. Don't push hard. Just slight pressure is all it takes. You'll notice the knife slowly begins to dig into the plastic and begins hollowing out a very small plastic crater that gradually get bigger and bigger. Resist the urge to push harder and go faster. You can crack the plate if you do. When you are close to going through the other side, flip it over and start there. This way when you break through it will have been from both sides. Going slowly gradually enlarge the hole from both sides until it is the correct size for the screws you are using. When done it's time for the bubble. Same thing just be careful, it's much more delicate. The holes in the plate I made large enough for the screws to slide through. The ones is the bubble are slightly smaller so the screws will bite.