Really wanting to get an under seat subwoofer for my 87 s-10 blazer, but the space is really limited. I wanted to know if anyone had any suggestions on what sub would fit there.

 

I had a 91 S-10 and had a custom box made for two 10" Kickers way back in the day (90's). It was with a 3-way ported chamber. I think thats what the dude called it. Always had people telling me how good my truck sounded, for not being an extra cab or having a box in the back with a shell.
But for under the seat?? Dont think you might have to much room..

 

You wont find a sub to fit under the seat.
Sorry to break the news. There is basically no space under there, especially to hide a sub in a box.

I honestly do not think you could even fit a 6.5" mid range under there.