Wisnewbee, could you please provide more info on your heater,thank you
I use a 48 watt proportional digital heater from the Incubator Warehouse.
http://incubatorwarehouse.com/48-watt-incukit-dc.html It holds a temp within 0.1 dregrees of your desired set point. You can control fan speed also. As the temperature in the incubator drops the heaters start to power up a little at a time. Say 10%. If the temp continues to drop the heaters gradually increase until they at 100% output. As the temp increases and approaches your set point the heaters drop output until it hits the set point.This is a complete unit. Heater, fan, thermostat and remote sensing wire. The unit only cost $49.99. It comes with the AC converter, but not the adapter to plug into a power outlet in your truck. I rigged up a DC power adapter for about $5.
I made my incubator out of a styrofoam cooler they use to ship medical supplies. I cut a hole in the side to mount the thermostat/heater unit. The sensing wire is on the bottom of the unit. I have created a bottom inside out of 1/2" hardware cloth. This allows for good air circulation. I made a bracket out of 1/2" hardware cloth on one side to hold a very large sponge. This bracket has a small metal pan in it to hold extra water. The sponge is soaked in warm water until saturated and installed into the incubator tray.
I fabricated small stacking trays with foam inserts. The foam inserts are about 2" thick and have 5/8" holes for the queen cells. The bottom of the foam has fiberglass screen hot glued to the bottom to hold any queen that emerges prematurely. The JZBZ cell cup acts as the cover. Each tray is made so that air can circulated around the open bottoms and each cell. If I could figure out how to post pictures I would. That would make it much clearer.
I've been very happy with the results so far. This heater assembly holds the temp so rock solid it's amazing. The temp varies maybe a couple tenths of a degree at most. If you want any other details just let me know what you want to know.