I see you are in Zone 6B, I am in Zone 5B. I use to play around trying to extend the season, but eventully gave up, since a lot of work is necessary, and the extention of the season was of marginal benefit. Now I just take what Mother Nature offers.
Sometimes, I cover garden plants in early spring, with mixed success. Usually waiting a week or so achieves the necessary result with no gamble. Last year (2007)I lost all my 22 tomato plants in one night, even though I covered with plastic, and after that night the weather was fine. My view is it is not worth the effort.
I like the barrel idea, particularly if they can be warmed during the daylight sun. I installed a small 6000 BTU, Natural Gas heater (Northern Tools) in my 6 by 8 Greenhouse for starting seed, with a heating pad. I can go down to about minus 5 degrees, if the plants are not near a wall, On some very cold nights in March, I also add a 700 watt electric heater with fan to move the air. Even then on larger plants, sometimes there is a touch of frost damage on some leaves.
The Greenhouse is only used from about 15 February until the end of May. I have given up on lights in the basement, since experience has taught me, that the greenhouse light is almost twice as good, once the plants sprout.The plants are much more healthy in the greenhouse with natural light.
My two cents worth.