With Saito 72, I ended up inserting the slim 5-cell 720 mA NiMH pack right under the stab, which achieved a CG 4.75" behind LE. I had to cut a slot right behind the former under stab LE. It was a snug fit with some foam. I then glued the cut slot back and covered it back up.

I thought the covering material is junk. Just tried to heat gun it; actually, don't do it. You will end up with worse wrinkle.