Hook your space heater up to a thermostat. Don't point the fan directly at one rack as the temps in this rack will be drastically different than the rest of the room. I'd actually get a few of the desk oscillating fans to circulate heat evenly. Do you have any back up plans if you loose power? Make sure there is a lock on your shed so no one can steal your snakes or other items. And have you made plans for summer yet? How are you going to cool?