As result of the work of @m26872 and @GertSanders supported by this community my "need" for a 3D printer is made redundant. The minimal boards like the My Slim 2AA Battery Node and GertSanders "One trick pony" make a housing superfluous.
Some minimal examples here on OpenHardware with 'real' hardware:
Standard (3/4 - 19mm) electricity pipe. Also fits a CR123 (3v) battery nicely.
Impact resistant (5/8 16mm) pipe (sensor powered by 2AAA/ or 2 'hearing aid' batteries.
An all nature housing in bamboo.
And the ultimate one, no housing. Hidden in the door and door post.