ecar, like what youve done so far, particular the raw ply- those possums (do they have names?) sure are part of your family..
Just thinking,...have you thought of a small piece of perforated ply?
It could slide in from the top (where you took the photo) and if you were to drill the perforations yourself, you could make a sweet pattern and design the position and the size of the holes to get maximum air, minimum intrusive light.
Not ply, just an image, so you know what Im talking about..
That's so sweet. 
I wish mine would play nicely, like that. At the moment it sounds like someone's being murdered, down the street, somewhere.
It's the warm weather, it brings out the grumpy in them. 
That's great. Usually I draw a circle with eight or twelve lines from the centre, then drill holes at roughly one centimetre intervals. Not very imaginative...
Names?
We started with Moreton, who liked muesli bars. Her little girl, Takeaway, came to stay. Takeaway's first was a boy, Kogan, and his little sister is MacBeth. Red is an old male who comes and goes as he pleases, and I think he's their dad. Actually, I think he's most of the possums round here's dad. There's a young male called Nuts, he has a sister called Mystery Girl (and she and MacBeth are firm friends). Vera, who I think is Takeaway's older sister comes and goes, and I think she is carrying a little one in her pouch but it's early days. And I think, but I'm not sure, that my dear little girl, Takeaway, is also in the early stages of motherhood.
Other possums come, and go, it's nice to see new faces even if they're only passing through.
I have a soft spot for Red. He came in one night, he'd hurt his back leg, and foot. He sat on the table under the tree and cried because he was in so much pain. I went out to look, and told him the possum house nearest the tree was vacant, if he wanted to use it. He climbed the tree using just his front legs, made his way over the pergola to the house, went inside and didn't come out for two days. He couldn't sit upright, on his back legs, so he couldn't use both paws to hold food. There goes picking up a piece of bread, or a slice of banana. I ended up making him finely chopped "everything" - bread, boiled rice, sunflower kernels, mushy banana. It didn't look too appealing, but he could eat it while on all fours. After a couple of days he moved across into the house in the middle of the garden and stayed there for a few days before he decided that he was fit enough to move on.
I've seen him a few times since then, he's looking good, the leg healed, he's doing okay.
It took me some running around to organise water dishes, and a little polystyrene plate for his dinner, but we made do.
I knew he'd move on, when he was ready. This isn't his home. It's a place he knows he's always welcome, but it's not the same as his place.
He needed help. What was I going to do? As I told him, there really is nothing I can do, but offer you shelter, food, water, and privacy. From there on, you'll have to work it out for yourself.
So he did.
That's like Mystery Girl and MacBeth - one big, one not so big.
Mystery Girl stopped to eat some sunflower kernels, MacBeth was right behind her, and rather wait, politely, she pushed her way under Mystery Girl, and then started eating, herself.
They're a funny pair, those two.
I've got a drill press, a drill mounted over a flat panel. I should be able to tilt the panel, then I could drill holes through it, at an angle.
I could take the existing panel off the house, drill holes in it, then put it back up, and save myself a "hole" (oh boy I'm funny) lot of work.
I just popped into the kitchen to grab a drink and the terrible two - Mystery Girl and MacBeth are out on the table, having something to eat.
Red's not a "Yes, I'd love it if you took a photo of me" kind of possum.
I produced the camera and he retreated into the house, leaving one part of his anatomy exposed, as a subtle message....
