It will be monday before I get the battery. So I will get it and test fit it and make adjustments as necessary.I can't remember if I made that picture to scale. What you want to do is see if a 2200 3s pack fits snug (not tight) in that slot. If so, then just put it in. I think I created that drawing as a reference.
That is correct, you leave the foam, but remove the top (or inside after the wing is folded) layer of foam, then wrap it around the middle wing piece. Helpful hint, glue the middle piece to the bottom section of the wing first (the one with the ailerons). Then fold the wing over and glue it to the center section.