Can the heaters be installed upside down? Can it be mounted on a hatch door?

Xtreme Heaters can be mounted in any orientation. Remember that heat rises, and the higher you mount your heater, the less efficient it will be in getting the heat down low into the bilge, where many of the components you are trying to protect are mounted.

If you must mount your heater upside down, try to direct the airflow as directly as possible toward the critical components you are trying to prevent from freezing.