For the lens, I used a 2.5mm lexan sheet for the gap. If you don't have that exact size, you can just mount it on the flat side. Those are pretty much unbreakable. You can buy these sheets at home depot and cut it to your desired size. The screws I used werem3 bolts. Feel free to comment on my design.

Update: Version 2 Holes are bigger screw will be flush on side gap is a little bigger

Version 3: realized that it back piece was snapping off pretty easily. It is now reinforced.