Double D

I have a 1987 190E 2.3-16V I wanted to know if there was a good way to mount a sub in the trunk or maybe rear deck. There is a full siz spare in the trunk covered by a mat that lifts up so nothing can permently be put there incase of use of the spare. I want the best way to put in a sub so there is no rattle and smooth bass. Any adivce I would be happy to hear. Thank you.
-Darren-