Very simple mounting bracket for internal drum trigger. You can mount it to your lugs on the inside.

Put a layer of neoprene on the trigger, put the baseplate over it, add a washer the size of your piezo element and put your piezo on top of the washer. Make a connection between the drum head and your piezo with foam. Try different types of foam and different pressure on the head for best trigger results. I put everything together with two sided tape, holds for years.

I made some with PETG, but I think you should be fine with PLA, the part doesn't receive a lot of stress.