Michael,
Power is great. ;-) Its also better to overpower rather than underpower. Underpowering means the amps more likely to run out of steam and start distorting, which cooks your speaker due to the DC current. Overpowering is fine unless you turn it up far too much.
1) I'd use a 12... a 15 is waay overkill, and are less accurate than a 12 (more mass to stop and start), tho its personal preference.
2) SVC or DVC makes little difference. A DVC sub gives you more wiring options... you can wire then in series or in parralell to give 2ohms or 8ohm. I take it your amp is designed to give most power into 4ohms? (a 2ohm load can make them *HOT*) A SVC 4ohm may be your better option here.
3) JL are good... but I've got a cheap tip here...
www.madisound.com is selling the NHT 1259 for $150. This sub is..... *awesome*. Its got a huge XMax, which is how far the cone can move outwards... Spec wise this thing kills anything below about $300 thats designed for in car. I use one in my spare wheel well, and its stunning.
4) 4ohm or 8ohm? Well look at how your amp is specced. 4ohm should be fine when running bridged. The NHT above is 4ohm
5) The thicker the better with the MDF. I use 1/2", but I braced it with hot rolled steel strips ;-). The less the board flexes the better. You may way to line the spare wheel well with carpet underlay (avaliable for $50 for a 30m roll....far cheaper than Dynamat etc etc)
6) The mesh just stops anything falling onto the sub... just a grill under the carpet. I can stand on the grill holding my girlfriend, so about 200lbs, and it supports this quite easily. ;-)
7) On the port, I think you really need to see what size will work in your car. With an NHT 1259 in my trunk, I found that 2 4in holes worked best. Experiment by removing the rear speakers one at a time to guess what size and number of holes you need. I think you'll be pretty happy with the bass..of course if you think you need more then you can look at putting a proper port there... (like 5inches or so of pipe..)
I understand about getting it right first time, and dont worry about all the questions...that is of course why this website exists ;-)
Bri
------------------
Brian Drought
1991 300CE
http://www.users.globalnet.co.uk/~drought/
ICQ: 2180069