Hi grover959, there are two circles at the top and bottom of the clear container. I rolled the poly-carbonate into a roll small enough to fit into the circle then slide the circles down to each end where there are screws about an inch apart driven into the circles. Marius Hornberger on YouTube has a great video showing a very similar cyclone,
I think the dogs like the windows too. I have often seen them staying in the house where its warm and watch me through the window as I go out to the shop, only venturing out if they know I am doing something in the yard.
I put a 'Hound Heater' dog heater in it along with a Wireless (Bluetooth) Temperature/Humidity gauge. I had no idea how affective the insulation was going to be and how much the dogs own body heat would contribute to the temperature. Turns out that I have not had to turn the heater on at all to keep a comfortable temp. I expect it would need to get down into the low teens before I would need to turn it on. Unfortunately my attempts to protect the Wireless gauge fell short and one of the dogs chewed it up ($25.00 down the drain). At least is served its purpose before it got mauled.