I would cut another circle out of a piece of material that would fit tightly inside the hole you have now ,thus providing a surface to secure to .
Or you can cut a bigger hole in another piece of material and secure it on top of your hole to act as a guide for a flush mount bit on your router and remove the excess material .
Is this a subwoofer box? I always do a test hole on another piece of material first. Once I get it perfect I save the plug for future woofers
I don’t always insulate , but when I do .
Ok ,I never insulate
Last edited by RainMan 2.0; 02-22-2020 at 07:10 AM.