You don't really need subs per say in your 04, but maybe a sub. One powerful sub powered by an decent amp should give you the bass you want and leave you useable trunk space. I just run one sub in mine with good success. One thing you have to take into account when adding subs in a vert. It's gonna sound bad a$$ with the top up. But the moment you lower the top, it puts a buffer in between you and the subs. They won't be as loud as when you have the top up. Just take that into account when you get subs.