No, I just filled two one litre bottles with water and lay them in their on their sides. Do this before you put the eggs in. Air changes temperature fast but water changes temperature slowly, so it just helps to stabilise the temperature against minor variations in the room temperature. They were slim bottles (milk bottles actually) that fit in the incubator lying down. If you had the incubator full to capacity, the fluid in the eggs would even the temperatures out for you, but I am making my first attempt with just a few eggs, while I get the hang of it.
If you look at the temperature and it has changed, usually the water well in the bottom has dried out, or the thermometer has moved. I am making more effort than usual to keep the room temperature stable by opening and closing windows and so on, and I think that helps too.
The incubator comes with basically no instructions, just a tiny paragraph on the outside of the box, so the people down the road have written their own instructions for the ones they sell. Fill the inner water well till day 18 and the outer one at the end of the hatch, that kind of thing - very much like a lot of incubators, but didn't come with the incubator.
I am going to build a brooder box soon, and I am thinking that if I design it cunningly, it can fit the incubator inside, with generous airspace all around, suitable ventilation and a hole for the electrical cord and so on. That way, if it does prove costly to run in winter, I can run it inside the insulated brooder box. Then I can take it out when the chicks hatch and use the brooder by itself. It's got to be at least as good as running the incubator in a cupboard, as was recommended to me. 
I was definitely looking at the cheap end of the market, and that contributed to my choice. I also considered home made. In the end, I thought that getting the parts for home made around here seemed tricky, this had all the parts (except turner, but there are home made turner options on this forum) and if I had to make some home made modifications, I didn't mind. As it is, the first eggs are coming along nicely so far, and I am happy with what I have spent, being a quarter of what my next choice in incubators would have cost me.