Notes:
To avoid supports, I made it in 2 parts. The TAB must be glued in order to fix it properly to the body of the case.
Bend the AC switch pins in order to make it fit inside the enclosure.

I have the 3000VA model, which you can find here:
https://s.click.aliexpress.com/e/_c4N6S9LH

AC socket:
https://s.click.aliexpress.com/e/_c34wdixv

AC Power Monitor
https://s.click.aliexpress.com/e/_c3MfsVYn

AC switch:
https://s.click.aliexpress.com/e/_c4U3dNEL

Cable rubber grommet:
https://s.click.aliexpress.com/e/_c3g4uSPZ

The fuse socket and the thermal switch is the same that came with the unit.