I ended up putting the two oldest birds in the cat crate. A little cozy but they got over it. So I might have to buy one more crate. I live in Walla Walla. About three hours south of Spokane. I can probably borrow one from friends also but thanks for the offer. The crates have to be small enough to fit into the prefab runs, about 2 feet tall. Or less. I am probably just overreacting but that thing freaked me out. :-(
My neighbors have chickens and chicks in some ramshackle enclosures, I will have to make sure I tell them about the possum. How do you say possum in Spanish? Maybe I'll just draw one. They'll get the idea.
You are not over reacting! There are so many horror stories, and the last thing you want is for something to happen because you didn't take it seriously enough.
Sounds like you can secure them for now in the dog crates, especially if you can find another one. Wish I lived closer, you could borrow mine.
I'd check Craigslist, and also perhaps post an ad on BYC's Buy Sell Trade forum.
I'd be sure to add a galvanized mesh apron to your coop/run.