Cheap vibration isolation for your couch/sectional for bass transducers!

I was looking online for a good solution for vibration isolation for our sectional. I was looking at bass transducers such as the Clark Synthesis or Buttkicker LFE. Both companies offer rubber solutions of varying expense, all far too expensive when you consider that my sectional has 16 feet!  

I started to think about caster cups as an option, did they make them out of soft rubber?  Nope, but then I pondered if i could put soft rubber IN them.  I had a workout mat which was perfect thickness, so I cut out a square and put it in the caster cup. BINGO.. this thing has lots of give in it in all directions. And it only cost a fraction of the price of the other solutions!