I would like to add something.

Wings get a bunch of their spanwise strength from the spars, right. And lots of them have shear webbing between those spars to get even more strength. But lots of fully sheeted wings get their strength from the sheeting. The grain of the skin does most of the work, but having the balsa there does the trick.

So what happens when a wheelwell does away with the continuity of the skin. Right in the area around the spars and where the wing sees the most bending stress, we hack a huge hole.

I always stick some 1/16" (at least) balsa in the wheelwell for two reasons. I fly year round and an opening in a wing can collect all manner of trash. And I like to know the wing skin that no longer is there to provide strength has something in it's place.

Here is a picture of the back of the wheelwell of a P40 ARF I did back in the summer of '06. I've wiped all manner of stuff out of it. You might even notice some wear and tear in the picture.

It actually doesn't take much time to do it with scrap balsa. With the grain sticking out of the hole, the stuff bends to the radius easy. Piece of cake. Cheap waterbase polyurethane seals really good.