IMO the only thing they need is something to protect them from predators.
They'll be fine in the tree all winter unless a raccoon or owl finds them.
As far as outside all winter. It gets much colder here. Below zero. An area friend has a nice coop and covered run. Roosts in both. Her hens chose to sleep in the run all last winter, only using the coop for laying, food and water. That's only one of the reasons (along with yours and many others' that roost in trees) I don't put much emphasis on the protection from drafts thing.
They'll be fine in the tree all winter unless a raccoon or owl finds them.
As far as outside all winter. It gets much colder here. Below zero. An area friend has a nice coop and covered run. Roosts in both. Her hens chose to sleep in the run all last winter, only using the coop for laying, food and water. That's only one of the reasons (along with yours and many others' that roost in trees) I don't put much emphasis on the protection from drafts thing.