Good idea but I have totell you that the 4 plastic screws that hold the rear cover on are NOT sufficient to hold any sub in place, especially over any sort of bump like speed humps or offroad. They also appear to become brittle over time as I have lost 2. I have heard the red ones are no longer available so I’ll be tracking down 4 black one’s on Monday. My sub kit attaches to the rear door with 2 screws to remove the weight from the plastic screws. Matching the plastic texture with gelcoat will be interesting - I look forward to seeing the completed project. Volume for a 12 and a 10 are different and technically not avail with the spare in the door. A 15” would be the perfect driver but certainly not possible with the spare