Tony, that's a really nice setup, well done.
I'm about to start converting my aquarium tank for use with FBT's and need to sort some sort of mesh lid out. It comes with a hinged, curved lid with 2 flaps similar to yours. My plan was to remove the 2 flaps and then cut out the centre section, then just cover all the remaining hole with mesh.
Have you done away with the original lid and got a separate screen lid to fit the tank? can I ask how you made one, or where you got from one if you bought it?
Causing me a bit of headache at the moment figuring out how to do it.