Hi, About polybox incubators. I have made my own and added a thermostat and used used two economy lights a 25watt and 10 watt bulbs added of course a computer fan for circulation. I have hatched many hens eggs and quail eggs, I have no problems with humidity as i find a tray that just about fits the bottom and put about 2 inches of water in. I have done away with the lid and just use a glass sheet added an internal thermostat and humidity reader, so personally speaking i disagree with most of the write up about them being bad to use. They are an economical way for people to be able to hatch chicks. But i would say that the temperature controller is important. I have also added a cut out at the top of the box, for controlled ventilation, which works very well and have added aluminium foil around the lights to reduce the intensity of light in the hatcher. I am personally very happy with what i have achieved. I also made my own candler for a few coppers!
There are some very helpful people out there that are willing to help you if you have problems. The poly incubator has bought a lot of pleasure to me and my family! I got the box free from my local pet shop I already had all of the fixtures. The only thing i needed to buy was the thermostat and that was only £9. So I am a happy chappy with what I have achieved.
Part of the fun is turning the eggs and to be honest there is too much fuss about the temperature being totally accurate. You just have to look at how a mother hen looks after her eggs, she will leave them too feed and have a rest from brooding, so a small deviation in temperature is not that important.
Good luck with your hatching no matter how you do it! :