Cat Litter BoxFan

(See the edit below)

We have just "inherited" a cat.
As she will be an inside cat, at least for a while, I needed to add a fan to her litter box.
Here is my attempt.
I was made a little easier as our inside gas hot water heater has been replaced with an external solar unit, so there is a ready built hole in the ceiling, and a chimney through the roof, but that is not connected as yet.
Having just junked a large photo copier that had 24V fans, a lager one was selected and it runs very well on 9V, nice and quiet.
An old "analog" 9V plug pack is used, and long wires are added to the fan.

To help get the screws from the plaster anchors in the fan, I ground the holes at a bit of an angle.
If you can get longer screws, they could be used to hold the fan assemble together as well as mounting to the ceiling.

Files here...
https://www.tinkercad.com/things/k4lszZJBi0R-litterboxfan
One on each end of the fan.

https://www.tinkercad.com/things/drmilVXqqDe-litterboxfanend
Mounte