Reoccuring Croup in 2 year old

My son is frequently coming down with croup, to make matters worse he has asthma so every time croup decides to strike, so does the stridor and we are rushing to the E.R because he cant breathe and starts turning blue on us. He takes a daily preventative inhaler, along with a nebulizer of albuterol for emergencies. Which if you are frequent croup parents you know that inhalers and nebulizers dont work for croup unless its epinephrine~..

They usually admit him, keep him for a few days while giving him epinephrine intravenous and by neb, and then send him home on a steroid.

We follow up with his pediatrician to be told to keep up with his Tx and if the worse happens again to go to the E.R otherwise steam the shower, or take him outside and give nebulizer Tx.

Thats all fine and good, until my baby gets sick again, and we go through these same things a month later. Im tired of him getting sick period....What is causing these reoccuring episodes of Croup...why is he so prone to it? Is there anything we can do that can stop the croup? or is there an underlying issue at hand thats causing it?

Any of all information is greatly appreciated.