Just a suggestion though, you might want to put some sort of retaining guide on the top of the shelf rails so your shelves won't tip when extended. Last thing you want is for the shelf to tip after you just spent 12hrs smoking a couple of hundred dollars worth of meat.
I apologize, I thought I was looking at a different build. You are correct, you can't really access the shadow plate once the BP is in. I've never seen anyone put holes in the shadow plate and I have never put any in my shadow plates. I don't think you'll need them, it's pretty hot at the throat.