don't skimp on the fan.. make sure it blows air so that it really mixes it up in the cabinet.. a lot of air movement will not hurt the eggs.. but it will prevent any unwanted cold spots..
any fan should run all the time in any incubator.. I have read about LG and Hovas coming from the factory wired through the thermostat..(wrong).. these have to be rewired.. very easy to do..