This is a modified base for this rain detector model, the author didn't publish with a remix allowable licence so I can't add it as a remix, but it's my own design anyway.

https://www.thingiverse.com/thing:4893894

The original model is for a Zigbee Aqara leak detector, but my model is to fit a SwitchBot Leak Detector.

The housing is a snug fit around the SwitchBot, with unfilleted bottom edges to aid printing also give a space for wires to pass around to the back of the sensor if that helps.

Print orientation is stood upright with the two screw mounts either side. You'll need supports to support the beginning of the outreaching rain sensor bracket arms, and probably to support the flat top section's beginning.

M3 recessed nut and M3 through hole for a bolt.

Also a friction fit rear panel and TPU gasket if you want it. The sensor is waterproof anyway so it doesn't really need to be that water tight, but if it was to fill up with water inside you'd get false positives. If you fit the rear panel with a TPU gasket, the mounting screws should be tightened so as to clamp the gasket and rear panel in place.