Well good luck.

Yes, the fabric would probably need to be heffty, mine is corduroy, to do the full back vent flaps.

Did you work the waist reduction into the vent seam? It would seem like a good place since you already have the seam open.

I very much look forward to finding out how you do the pocket flaps. Those are the one thing on formal jackets that I don't quite understand yet.