I am totally enamoured with our Ecoglow! That thing is completely amazing! Our chicks huddle under it then dash out to eat and return to snuggle up for some sleepy-time. It's fascinating to watch them - better than water-bugs on a lake!
If you're concerned about weather - and not planning on moving the tractor part often for the first week or two - take bales of straw and place around the outside of the tractor/hoop house - it'll add a layer of protection against elements. Now, this will take a bunch of bales - so it's not practical for everyone. But it does keep the drafts down considerably.
The other thing that keeps drafts down is plywood sheets - I've placed a full sheet of ply against the side of our PVC 'tractor' and the birds really seemed to appreciate the lack of draft from that direction....all heaped up against that side of the tractor snoozing peacefully with full crops.
Truthfully, a hawk won't be able to take a full-sized CX, so after about 6wks, they could have more space out in the open. But they'll do very well in something that size.
Enjoy 'em!
(edited to add: a plus for the bales of straw - they can be used as winter mulch once the chickens are in Camp Frigidaire! Although our bales of straw two years ago had too many seed heads in 'em, and we had a nice mini-crop of wheat that summer! Bah!)