I did the bass drum a little different I used the same method I used here to support the peizo sensor. I scraped all the coating off a CD disk. I cut to size and super glued it to the wood. I wanted to make sure I had a nice flat surface and the 3-M double sided tape stuck well. Then I cut a circle of 3-M double sided tape the size of the ceramic and attached the piezo to the top third of the CD disk. The drum pedal beater will hit right in the middle of the CD just below the sensor. There are many listing for piezo sensors on Ebay.
Added more 3-M double sided tape to the piezo and CD disk
Remove the sanding surface from the foam sanding block and stick the whole sanding block to the 3-M tape.
I have been using my Roland KD8 for about a year now and I really like the way it feels. I was surprised how good the bucket bass drum felt. I could hardly tell the difference between the KD8 and the bucket bass drum.