It is really easy. here is the way my buddy and I did it.
1- remove the carpet from the side and layer it with 2 layers of tape and then one layer of tin foil. (so the resin doesn't ruin the carpet, cause mine is not really a part of the trunk it is removable)
2- put a layer of fiberglass down then resin all over it, let set up for like 30 minutes then repeat like 3 to 4 more times to get a good solid box.
3- once it has set and is completely hard remove it from the carpet then cut a piece of wood for the front. then fiberglass the holes around the board so its all one solid piece.
4- drill in the hole for the sub and use a flashlight to check for thin areas. hold the light inside and shine it around well looking outside to see if there is any holes or thin spots.
5- if its all good then wrap it in felt with resin and then carpet it. if you want the cool G6 logo in the carpet, then just cut some foam and glue it on the felt before the carpet.
6- then run some wires mount the sub enclosure and enjoy.
Hope this helps, any other questions feel free to ask.
Pontac G6 Sedan 3.5L
Exterior- 8000k HIDS lows, 8000k HIDs fog lights, 20% window tint, Tinted taillights, painted grilles (top and bottom) to match, Custom painted engine cover and battery box, Red painted calipers.
Performance- Crab Intake, Racing Line Performance strut tower brace, GT-R Custom Magnaflow exhaust.
Interior- red LED's on inside, custom painted interior trim to match outside, Memphis sub and Amp, Custom fiberglass sub enclosure.