Waterproof is a binary concept...
So, the roof on the back side of my house has a couple of "V" angles, and the snow and ice builds up.
A couple of years ago the roof leaked, and the main family room need a new roof, new sofa, new carpet...
I put a heater cord on the roof and wanted an outdoor thermostat to turn it on and off.
No use running the heater cord on the roof, to melt the snow and ice, when it was warm enough that the heater wasn't needed.
It was a bit of a quickie, "weekend" project, and my goal use to use up a few of my old through hole components, as more involved projects are all SMD these days.
This was a quickie DS18B20 digital sensor, relay, LCD for fun, and a Tiny. Not much too it.
The project has worked fine for the past three Winters.
I went to go plug it in for the Winter and was dismayed to find that my Water-Tight, Weatherproof case wasn't so water tight after all.
Mechanical aspects of project design, and cases, have never been something I've excelled at.
Fortunately, I dried it all out and it works fine.
But I'll have to put it inside of a protective enclosure outside.
Original project, nearing completion.
Shot of roof, with heater cord melting snow, shot through a screen.
Three year's, post install: Not looking so good...