Maybe this will give you some insite. try using the Golden Ratio method. I have played this this with success. 16' x 26' x 10' is a nice size but you can do some math with what you have and get close. Decoupling the floor will remove vibrations from other places in the house. Rubber spacers are used in some recording studios. Check out the forums on recording.org if you want more detail.
http://www.cardas.com/content.php?area=insights&content_id=26&pagestring=Room+Setup
Mark
http://www.cardas.com/content.php?area=insights&content_id=26&pagestring=Room+Setup
Mark