I designed this to mount a light on a flat surface and allow to enclose a 12v rear light with brake light purchased on Aliexpress.

(this is the link for that light: https://www.aliexpress.com/item/1005005191784894.html)

It fits the small light snuggly and has an internal path for the cable which guides the cable to the side.

Three tiny holes are present to fit very small M3 inserts to be able to bolt it on or under a rear fender/mudguard. This is meant to be bolted to a flat surface.

A cable can be inserted from the back, and some epoxy glue may be used when pressing the light inside after soldering the cables to prevent any water ingress.

(this is the link for the cable: https://www.aliexpress.com/item/1005002823599737.html)

I printed this vertically with supports in ASA.