Posted for "Jim Nordin" <panelmaker@earthlink.net>:

 There's plenty experience with this kind of thing and here's mine.
 
 I'd make the hole oblong just larger than the existing hole. But oblong by
 1:1.5 to the original hole size.
 Make a replacement piece of laminated foam that will go inside the wing that
 is 3/4" larger in all dimensions of the oblong hole you just made. By
 laminated foam I mean a piece of wing quality foam that has been laminated
 with the appropriate number of layers of either glass or carbon fiber
 depending on the makeup of the original wing skin. Make the inside (the fuel
 tank) of this skin pretty wet for purposes of fuel proofing.
 Make sure there's 3/4" or more lip that has no foam on it so to use that lip
 to bond to the inside of the wing skin.
 Scarf the top wing skin hole area 3/4" or so to blend the replacement skin
 with.
 Clean the inside of the skin where the bond will attach. Bond that
 replacement piece in with hysol and let cure.
 Now fill all around the foam insert and the area of the damaged wing with
 the appropriate filler but don't fill it to the top level of the existing
 wing skin. You can fill after this cures and not take the chance of cutting
 into the fiber.
 Layup the appropriate number of layers of replacement skin material on the
 replacement material and scarf to the top skin after cure
Fill, sand, prime, paint.
 Good luck.
 Jim
 

"""
 Does anyone have any experience/suggestions on how you would fix a serious
 Ding in an upper wing skin.  By "Ding" I mean a 3" hole/crack all the way
 through the skin (outer/core/inner).  Assume the hole/crack is over the fuel
 bay and inaccessible from the inside/bottom.
"""