Had to break down and get some of these: the nights are just too cold for my tomatoes.
This is one of those great ideas I like to discover. The natural physical properties of water to hold heat and discharge it as it cools, the weight and resulting stability of the structure: it’s just a great idea. I wish I had heard of them 2 months ago.
I have 8 of them out (they come in packs of 3 at your local gardening outfitters: I found them at Lowe’s), so I have one in reserve.