We've had a couple of nights when the temperature fell below freezing but I've found some ways to add enough heat to the green house to avoid death of my tomatoes. The first night I found out rather late in the day that it would freeze. I quickly set up a little charcoal grill that has a domed cover. We lit it and the following morning I found that most of the briquettes had been consumed, but not all. Although I plan to eventually install the necessary heat and smoke dispersion to my chimenea, for now I found a room sized convection heater for less than $40 at Home Depot plus a 'Frost King' regulator plug in that will start the heater when the temperature drops to 35 degrees and stop the heater when the temperature raises to 45 degrees. This will save on electricity costs while keeping the killing frosts at bay. It is 'hard freeze' that kills plants.
I also purchased four workshop 2 tube florescent light fixtures and a box of daylight (6500 kelvin) bulbs to add an additional amount of light and some heat directly over the grow bins.
I plan to plant lettuce, peas and spinach in rain gutter trays that are heated with a warming cable meant for seedling trays. These are intended to be like the display at Green Sky where the water trickles down the gutter and discharges into the fish tank. After looking at the price of 'rock wool' growing bricks and other alternatives I am using coco fiber in my grow cups. This came about when I found a super sale on some hanging baskets furnished with coco fiber.
Meanwhile I'm making a mad dash to finish up my 'winter coop' which will use black painted tubes filled with water to gather heat during the day as well as a solar panel to run a fan and light. It will be interesting to see how I get through the impending winter.