I noticed pioneer woofer on my 92 SC4 is weak. What are my options? I would like to add some oomph w/o adding a big box in the trunk. Can I add aftermarket 10'' woofer? Any recommended model? Do I need a separate amp for it? Thanks in advance.

i have one i purchased off e-bay. when i went to change mine out, mine was working fine.
if interested in a stock pioneer 10 in, search site it is listed.

any 10'' sub (shallow mount to be safe) that is free air will work just fine. I would recommend an aftermarket amp.

I have a 10" sub in mine right now in the stock location. Its a Pioneer TS-W252R. I had to cut a piece of wood to put underneath it in order for it to sit flush underneath something since it was too big.

You will need another amp to just power the sub. Here is a pic of mine in the car right now.

^^ i really like that.. but theft is one of my main concerns here

It's possible to do a shallow mount sub in the stock location, however for the best possible sound quality it is still best to have a sub in a box even if it's not a large one. I have done a free air setup in a 1990 LS and a 1999 LS and the subs sounded okay, but I was never totally satisfied. I also blew one sub by causing the cone to travel too far and the sub locked up. Free-air environments allow the subs to move freely and most subs aren't designed for that.

I finally gave in and did a sub in the trunk and have been very satisfied.

Here's a small box I drew that gives the sub approx 1 cubic foot of air space and fits nicely in the corner of the trunk. There is also a similar box on eBay which offers .6 cubic feet of air space. The box is easily removable and uses very little space when compared to a traditional sub box.

Is there anyway to build a shallow but long box under the rear deck over the tank? Been an Idea of mine for a while. I dunno if it will work. When I get back to the states I will work with a box builder, and see if it can happen.

It may be possible, it'd be an extremely tight fit.

DLS OA10 300RMS @ 4 Ohms
w/ a 300 Rms amp
Get it it rocks you'll be happy

Thank you Believe me theft is one of my concerns as well. The car sleeps outside in an apartment everyday but I guess I'm in a better part of Tampa so I should be ok (knock on wood).