I could sell you the fender sub that I might replace with my JL Audio stealth box.
On the other hand, I have two small kids in the back and my wife would prefer I not shake their brains around so I haven't bothered installing the stealth box. It came out of my 2012 JSW and I'd be willing to sell it. Market value is somewhere around/little less than $500 since they were $900 new and discontinued. I used it for about a year before the buyback. You'll need a LOC, but I have the one I bought for the job available that'd go with it.
Last option would be what I did for my bug, but I don't know if you're going to like it...
I had a JL Audio 12w7 and commissioned a local pro I knew to hand build a fiberglass tub that fit into my spare tire well. I removed the trunk deck and installed a false floor with metal grating. I might be able to take some pictures tomorrow if I get home early enough, but if you want to see them and I forget shoot me a PM to update this thread over the weekend.
Now, the sub will knock a hole in the car's roof and blow anyone next to me a lane over but it cost well over $1,500 for that one speaker not counting amp or wiring or anything else in the system, which is why I said not sure you'd like that solution. Takes a real dedicated enthusiast or dumbass to dump that much money into a 98 that is too much work to remove pre-sale
Luckily I did it before marriage because my wife doesn't have to vocalize which category she feels I'm in for me to know