Disclaimer: I’ve never tried what I’m about to suggest. No promises that it will work, but it seems to me to be a good option.
The Fibaro door sensor has an auxiliary thermometer input which you could connect to a waterproof temperature sensor. If you end up exploring this option, make sure you purchase the first generation Fibaro sensor, I don’t think the newest one supports the auxiliary input.
Here is a thread about getting the Fibaro sensor working with SmartThings.