For the bottom cover use at least 3 walls because the 2 rods holds the whole light together.
When slicing, stick to the foto in galery.
Assembly + installation:
You can optionaly print the template to help find holes to drill.
Assembling beggins by putting and screwing the E27 light socket inside of the mount + route the cable into the mount hole at the bottom.
Close the bottom of the mount with bottom cover by aligning the 2 rods into the 2 holes of the mount, also when closing you will seal the cable hole so make sure the cable will not be damaged.
Attach the Top cover part to the top of the mount, again align 2 holes of the top cover with the 2 rods.
Screw the 2 nuts onto the rods so all the parts sticks together. You can optionaly print the key which helps with screwing.