The last could of years I have brined the Turkey then shoved apples inside of it just to have something in there when I smoked it. I've seen a couple of people talk about putting an onion, a lemon, and rosemary etc inside the Turkey when smoking it. Do you think that actually affect the flavor at all, or is it negligible?

I think it blocks the smoke from getting in there as effectively as if the cavity was empty. I also think it would cook more evenly without being stuffed.