It's a simple 3/4" pine board, but additional strips around the edges to exactly hug the cabinet, cut at an angle where necessary. Then plywood underneath as well to hold against the inside of the cabinet corners (cut at an angle as well). Hooks will go into the plywood to hold it down from inside with turnbuckle bolts. A groove is routed in the one side for the front edge of the glass to slide under it. I'll put a bit of foam weatherstripping in that groove to pad the glass.
Every edge is heavily rounded over with a simple router roundover bit so it feels nice to wrap your hands around the edges.
It fits quite snugly. I can access the holddown inside through the passive air intake hatch you can see in the third picture, which I sized large enough to easily fit my arm into since I have no coin door.
Please let me know if you have questions.
Edited by stevepax, 17 May 2018 - 04:03 AM.