This is not a dumb question, it’s a very reasonable one!
The first part of the answer is that you’re not supposed to make yourself sick, or suffer, for the sake of Judaism. So if it’s raining or too cold, you definitely don’t sleep in the sukkah.
We live in Portland, OR, so sometimes during Sukkot we’re in our rainy season. When it’s not raining, though, it’s usually in the 60s and 70s during the day and gets down to about 50 at night, so if we wanted to bundle up or bring out a space heater, we could.
Mostly Spider just takes naps in his hammock during the day with Rumba though.