Was waiting on someone else to reply but there is my thoughts on the matter. The big advantage to Coelan is it's flexibility and high UV resistance. If your under coating with something else less flexible your have lost half of it's advantage, the coating will only be as flexible as what is under it.

(Are they even compatible? Can you over coat with Coelan? I don't know)

Second, if your not going to keep your boat outside in the weather you have lost any real advantage to me. Unless someone has another reason I am missing, I wouldn't do it.