I think I've seen socalwarm's greenhouse at Big Lots. I'm pretty sure it has a zipper-type door that opens to vent. I would like to have a quick set up green house like that, but I get high winds on top of the mountain here in winter, so I have to have heavy frame work for my coverings. I use black plastic garbage cans, 32 gallon, and spray painted some 5 gallon buckets and some gallon milk jugs to pack around my trees in winter. The black paint flakes off after a few years but so what. I have found that unless the water container is right up against the plant, there is not much thermal protection/ benefit. The plant tissue higher than the top of the water barrel tends to die off with the deep freeze. I've also noticed that when it is extremely cold, single digits or zero Degrees F, unless you have a heater in your plastic covered enclosure, the temperature in the enclosure will drop a degree or two every minute or less even with water barrel and jugs of water in there. Water barrels help some, but I don't think they are as influential as as they are touted to be,at least not in extreme cold situations. I still do them anyway!