I used mechanical thermostats where I bought around a dozen from an online electronics retailer. Maybe they are difficult to get, nowadays. Those thermostats I've put into a plastic case from the same retailer and there was one mains cable into such a box and one out, with a mains socket, so I could connect whatever I wanted: one bulb or more or something else.
Only the cabling with those thermostat-boxes took up some space in summer. I had always about a dozen shelters "to maintain".
Where we live now we really wouldn't have all that space, but winters are quite milder now so we don't need it at all.
Then I stored ...
wooden frames of sizes 1 x 1 meters and 2 X 1 meters. Then different material to attach to the frame, mostly plates of tri-plane, and bitumen roof plates, and the like. This was a great mixture of everything I had already lying around or I could gather relatively cheap.
The so constructed shelters have been made a liitle bit more air-tight with one or more layers of plastic foils, tent-flats and the like. A cord around them and also further cords to secure the whole thing against strong winds held the entire construction it its place.
I must add that most of the shelters were in the backyard so the ugly collection of strange objects didn't disturb my wife too much as the neighbours already knew that I was crazy and worked at night in the garden when it was really cold or stormy.
The more solid you do those shelters the less work you have with them, the better they look and the more they will cost.
And one important thing is: lots of thermometers, at best those min-max ones, to get an idea how good your shelter is. Thermometers on the ground, on the stem, in the crown ...
