I know that one day I'm going to pull away while the antennae is still extended. To prevent this, I have tried to get into the habit of retracting it before I go out to do other things the morning we are leaving.
It's a simple process. From within the trailer, I simply turn the crank to lower the antennae so that it is flush on the roof of the trailer. If we have turned the antennae in order to improve reception, then I line the markings up before cranking it down.
Once I get outside, I take a look to ensure it has, indeed, retracted properly. If I step far enough from the trailer, I can tell if it has retracted.