Setting up a thermostat in a still-air incubator

Okay, for the hatch-a-long, I decided I'd buy a thermostat for my still-air.

I'm trying to get the temperature regulated to be 102 degrees but it seems so far that I can not get the thermostat to hold such an accurate temperature.

1. Do I need to convert it completely to a forced-air incubator in order to get a thermostat to be precise?
2. Is there a specific type of thermostat that I should use? I am using a water heater thermostat.
3. Am I going to need a thermocouple for this?

I have not modified my incubator at all. The thermostat is laying in the back of the incubator and inside of an old squeeze bottle in order to keep the chicks from getting fried on New Year's Day. That would be a horrible way to ring in the new year.

I've taken the thermostat out of the squeeze bottle for now though, since I don't have eggs in the incubator yet, so I'm hoping that will make a difference. I am not sure where the thermometer is on the thermostat so can't really tell if it's because the thermostat was not getting hot as fast as the rest of the incubator or not.

Thanks in advance for the help.