Here is a heater that I built for my home-brewing fermentation chamber. I use a chest freezer for my fermentation chamber. I needed a small heater for a 2 stage temperature controller that I purchased. Cooling is handled by the freezer of course but a small heater is needed inside of the freezer should the temp get too low.
I found this idea in a forum and copied it as best as I could.
I hope it is helpful
Step 1: What You Need
I believe that everything that I used is show here.
1 empty paint can
1 ceramic light fixture
1 electrical mounting bracket
1 lamp cord with plug
1 light bulb (I have w 60 watt bulb)
2 small nuts with bolts
1 drill with bits
1 wire cutters/strippers
Step 2: Mount Bracket to Paint Can Lid
Using an appropriate drill bit, prepare lid with holes that align with holes on bracket. Be sure to center the bracket first. Use your bolts and nuts to securely fasten bracket.
Step 3: Add Cord
Drill a hole for your cord thru the paint can lid. It's easiest to use an existing hole in mounting bracket.
Work your cord wire thru hole.
Prepare wire ends for light base.
Step 4: Wire Ceramic Light Hardware
Simple enough, right? Just be sure wires are securely fastened.
Step 5: Final Assembly of Light Hardware and Test
Attach ceramic base to bracket using screws that should be provided with bracket. Pull cord taught thru hole in lid as you assemble.
Screw in your light bulb.
Plug in to test.
Step 6: Reassemble Paint Can
Replace lid with light assembly to complete this project.
Note: I drilled a small hole in side of can so that I could see that it was on. Not necessary for all applications.