Out of interest, your cat flap seems to have exactly the solution I'm looking for... Care to post a few more photos of it or let me know how it's been done?
They just added a U shaped spacer made out of wood to level the surface. The flap itself has plastic tunnel that goes all the way through. It's not particularly well done.
Posted this in the wrong thread. Duh. Cross posting here.
Any recommendations for improving the weather resistance of this door set up?