not bad but delicate fixing ...

a painful default anyway: if you want to set the cat flap by drilling holes, you can not see the hole locations (opposite side) on the hull of the object and it is necessary to calculate its really good time! (So ​​that the holes in the wall you do coincide well with those already made on the inside of the flap).
The simplest seems to try to embed it and stick with super glue ... but will have to see how it fits in the time ...