That's great idea. Isolation makes all the difference too. When you mount anything rigidly to your frame most of the energy is lost to the frame and you don't feel it. Having two transducers on your seat means you can dedicate them to different effects and work together at times.
I 3D printed mounts with a large 8mm bolt and a captured nut. There is a piece of surgical tubing around the bolt where it passes through my pedal plate so it doesn't grind.
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Edit: 6/12/21 Added a shorter left and right plate support that can be used when vertical clearance is an issue for the taller supportsThis is an isolation system that allows a sim racing foot plate to move well isolated from the rest of the rig. This captures the Sorbothane so it doesn't...
www.thingiverse.com
The transducers are mounted directly under my heels.
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My seat mount is different because I have a seat mover under my seat, but directly mounting to the underside of your seat works the best.