A weatherproof outdoor enclosure for a Tapo T110 contact switch, which I use on a gate. This fits like a glove. Box and Lid printed with PETG to withstand the elements. I printed without support, so the hex nut recesses on the underside turned out a bit messy, but still good enough to push the nuts into. The gasket is printed with TPU 95A. If you don't want to print the gasket, you could instead use 2mm diameter rubber or silicone sealing cord.

The bolts are M4 x 20mm hex countersunk, which each fasten into a hex nut, fitted flush into the underside of the box. See photos. I sourced the bolts and nuts from Amazon.

There's also a housing for the magnet. This can help you to position it closer to the switch, if your gate has a wide gap. The dimensions of this worked for me, but requirements may vary depending on your setup. I recommend printing this part with support, because of the magnet recess.

This version is designed to be fitted onto the gate and post with industrial-strength, double-sided tape. I'm considering another version with screw flanges.

One more thing... I found with the Tapo contact switch that if it's mounted too close to the ground, the radio signal is reduced a lot. When I raised it from 180mm above ground, to 680mm above ground, I got a much stronger signal.