Stuff you need:
-Quality Street Tin Lid/ something similar;
-1/4" Mono Jack (http://www.maplin.co.uk/3.5mm-monochassis-socket-1152);
-Piezoelectric Transducer (http://www.maplin.co.uk/piezo-transducers-3202);
-Drill with drill bits capable of going through thin metal. (1/4" and 6mm drill bits needed);
-Double Sided Tape;
First, cut the mouse mat so that it covers a third of your tin lid.
Next, stick it onto the tin and secure it firmly.
Now, solder the wires coming out of the Piezo onto the jack, and make sure the join is secure.
Stick the Piezo onto to bottom side of the tin, near the centre of the mouse mat.
Drill a 6mm hole in the side of the tin for the Mono Jack, close to the Piezo, and mount the Jack in place.
Then drill a 1/4" hole in the top of the lid, roughly in the centre.
Finally, mount it on the tripod, connect it to your module and blast away! :)