Ah.... a brooder coop. Ventilation is different than air flow. Its more important to have fresh air than warmth. Many broodies dont set through the winter. Even so thats what the hen does Keep those chicks warm when its cold out. Better to have more ventilation than you need and just cover the holes. The biggest killer in winter time when its cold out is humidity.... that's one of the biggest reasons for good ventilation.
WRT broodies.... The breeds of birds that lay the most eggs usually are not the best broodies... Most are non setters. (There can be exceptions.) Because when a hen goes broody she will stop laying eggs. So for instance if you wanted to breed Australorps a good idea would to be collect those fertile eggs and give them to a broody..... Breeds of birds that often go broody? Game Game crosses Cochins Cochin crosses Silkys ...
For a broody hen I have seen the best setup is for an individual hen to keep other hens from adding to her clutch.... Some will pancake down and not move when another hen climbs in on top of her and lays an egg. The broody will then move that egg under her.... Problem is the eggs under her are already developing.... The new eggs get rotated in and if there are too many one will pop out and get cool so the hen will rotate that in....
I had a hen once I found on a nest in the dogs house.... she was a bantam Americana cross. She must have had twenty eggs in there.... Only four hatched. If I had found her when she had just started setting and excluded access from the other hens she could have hatched out at least ten. Afterwards that dog house was the bomb for the broodies.... LOL. I just made a chicken wire cage around the whole thing with enough room for a feeder and a waterer and a place to dust bathe. If I lived in a cold climate I would have a walk in coop. I would have set the doghouse in there and set up a broody area. But I dont. My coops are chainlink with tarps over the top. So the most protection I have is for the wind.
Sorry I wrote a book.
deb
yeah the ground is really dry here too we used a jack hammer to make our french drain because the bobcat couldn't do it! DH thinks that we can use a tent peg to ground it when it is at our friend's house who will most likely look after them, their lawn is wet because they use sprinklers a lot. She will be fine putting in a steel tent peg but probably not a series of stakes. I didn't want to attach it to the coop itself because it is being heaved in and out of a pickup and carried sideways through a gate and I just know something will get caught. 
