There exists 2 versions of the 3.5" PiTFT with different dimensions. I got the version with the PID 2097 and not the newer PID 2441. So the OctoPrint housing was no good and I was glad to find the Touch Pi housing (https://www.thingiverse.com/thing:653291) from adafruit.
I changed the bottom stl, so a raspi3 could be mounted and added blocks to fix it on the wall.
Fortunately there is enough space and the possibility to add a switch for the backlight.
More infos on www.weigu.lu.