They're pretty simple, just a box with a rack, a fan, and a heating element.
Step 1: Ingredients
AC 220v computer fan
Light on flex
Pliers / snips
Coat Hangers to make rack
Glue, not pictured
Step 2: Wiring
The fan is a 220v AC fan, so can be wired straight to the plug.
I removed the bulldog clip at this stage.
Step 3: Wire It All Up
Step 4: Test
IT'S ALIVE !
Step 5: Making Some Holes
Carved it out with a craft blade and a knife. The knife was more effective.
Step 6: Some Cracking
The dog in the last picture was super critical.
Step 7: Mount Light and Fan
Fan was mounted with glue. Tried superglue first, but it cracked off, so ended up using Tec 7.
Step 8: Take It for a Test Drive
Lid is left slightly ajar at the opposite end from the fan. I may make a vent if this doesn't work properly.
Made a rack from the coat hangers in the first picture.
Lined the bottom with tin foil to catch any drips.