Barrels of water are an cheap, easy to set up, and surprisingly efficient way to keep the temperature high under a enclosure. In last 4 years i have been growing a mango in zone 8 with nothing else than barrels of water (around 120 gallons) to keep it warm, and sun during the day to warm the barrels. And i live at 44N so my sun is pretty low during winter, night are pretty long, and also since i'm in a mediterranean climate, often overcast. Still...
The principle to give minimal effort is a good one. Over the years a plant has to prove itself Exceptionally Good and Worthwhile to justify all the time spent, and the effort done to keep them alive. Eventually the novelty effect wears out, so you'll be willing to do so much effort just if the plant is really good, or the effort is sustainable - evenmore if you plan to grow several plants.
However when attempting something hard (like growing a plant outside its growing zone), i think that first you've got to attempt to reach you goal, then simplify. For instance the first year with my mango i used 1 gal container to store the water instead of barrels because the 1 gal containers were more efficient (in my imagination) for heat exchanging. They may have been; but the work of filling then one by one was simply too much time consuming and tedious; so the next year they were gone. The plant survived and i got some simplification.
Of course simplification can't go on forever, but you get the idea. You get your plant to live first, then you try to push the most lazyness it can stand before dying.
