Holes, and a button.

Found that the best way to drill into tin was to use a wood bit.

Cooling holes drilled for the fan drilled off center so that the air should blow on to the main heat sink.



Some holes for heat to rise out.



The shiny button installed.



Also, given my circuit idea some more thought, and if the ground is common then this should work and simplify the design. This hopefully is the final final iteration before I break out the soldering iron.