I have printed this with a high infill as I'd like it to be strong, you can probably use less.
After the mod was printed, I placed the door into the mod then sanded it with 80, 240, 400, 800 and finally 1200 grit sandpaper before painting it with an enamel paint.
The original design of this is a derivative of the Dinky Cuboid found here:
I originally used a printed version, take measurements to make a more print friendly 18650 mod.
This time i've started with a piece of paper and created my design in pencil, before designing it in FreeCad, using the dimensions I found appropriate for the mod I wanted to make.