I hear you... I know what it is like to keep temp low so it won't spike.If I didn't have such a touchy, temperamental incubator I would do that too. With my luck it will spike a temp and kill all my chicks!
Then I bought a $14 thermostat and put it in a $10 styrofoam cooler and it seems to hold temp better than a lot of incubators. I did buy a $10 fan too ; )