Johnson marine toilet flush button casing

The push button panel on Johnson electric marine toilets have te be mounted flush with the wall. I have made an casing to mount it on top off the wall, eliminating making a hole in the wall.
The casing features 5 mounting holes for mounting it in the wall and 4 mounting holes to mount the button panel on top of it.
The 4 mounting holes of panel are 45mm (width) and 83mm (height) apart. The casing is 21mm deep.
The sqare hole for the cable tray is 14x10mm

link to user manual of toilet: h