Here's a few more pics:

This was the first tumbler that I built.  It has two fans when only one larger one is necessary. Note the dangerous lack of fan guard! It uses a 2 speed evaporative cooler motor.  The switch plate was made by a local photoetching business for a nominal fee.
This is a shot through the rear vent showing the motor, disc and how the motor was mounted to the cabinet.
Here's the plexiglas top and the back of the unit showing the rear vent.
Here's the plexiglas top removed from the tumbler and held to the disc so you can see the clearance.  I painted the disc/magnet assembly so it is difficult to see the magnets.