My now 29 year old son had croup twice a year like clock work from the time he was 1 until he was 4. He would feel it coming on and would cry and say "I'm getting the cough". Broke my heart.
Back those many yeas ago I was told to take him outside in the cold air. It was especially good if the air was misty. So that's what we did, worked really well.
We rushed him to emergency the first time he got it too, worse thing ever!