Help with custom HOME sub box out of a JBL LX66

[Ricky Reboot Dean]

I was helping my grandmother clean one of the properties she manages and had to throw something out. I found a single JBL LX66 box with a missing 8" driver and the other one with foam rot. The tweeter and mid-range still look good. I wanted to seal up all the holes in the box to use it as a custom sub box for my home 12" subs. The box has a few circle holes in it and they would fit. I was wondering if anyone had any advice on how to seal up the existing port and other various sized holes in the box. I already know I am going to have to cut a bigger whole to get the 12" subs in. If anyone has any other advice that is easier than cutting plywood to almost match up 100% than use a sealer around it that would be helpful. The sub I am throwing in are Celestion G12M-70. They are old but look and sound great. Just need some help to get it started. Already am working on a few minor fixing projects this is going to be my first build to create something 100% custom using a already pre-fab box. Any help would be appreciated. Budget is limited so nothing overly expensive. Also if anyone thinks this amp Harman/Kardon AVR 20 II is any good tell me. (I already own it paid 60$ for it no remote and no rear channels, don't need either anyways).

[Soccerballzs]

Make a whole new front of box wrap in veneer tape and and stain black then lacquer