Here's a pic of an incubator I just got finished. Just in time for some more monitor eggs.
I wired an AC fan to run 24/7 to move the air around.
Also the heat is supplied by flexwatt.
Here are some important details for creating your own incubator.
For flexwatt ; 10-15 watts per cubic foot of space.
Fan ; 5-10 cfm per cubic foot of space
The flexwatt is simply wired in series.
I have it plugged into a Herpstat thermostat for control and then into a UPS backup power supply.
Note that using a UPS you need to have a Herpstat brand. The others won't work with it.
You need to have it in non-proportional mode.