After checking out Barry's video review of the Sim Racing Studio ShakeKit rumble seat pad thingo, I started to research the Dayton Tactile Transducer pucks that he revealed to be used the SRS product.
I decided to buy 4 of the Dayton pucks, a cheap USB soundcard, and hunted down a 2nd hand sound system amp to drive them. I DIY'd a solution to mount everything under my wooden seat box that I have my scavenged car seat bolted onto. The project wasn't very difficult and the results really impressed me. I found that the amazing SimHub software did everything I needed and more. I've since started using SimHub to drive the dash I display on my old android phone too.
I now can't imagine sim racing without the tactile feedback that the Dayton pucks provide.