Curt,
   When we discovered a few small bonding voids in my wing closeouts (using
a simple tap test), we drilled some small holes a few inches apart in the
skin above the cap strips and pumped in some hysol with a large syringe.
After putting some weight on the skin until the hysol dried, we filled the
holes with flox and bodyworked them over.  You can use the fuel cap hole to
get a flexible shaft flashlight and a mirror in to check for some
squeezeout.
   Skip Slater
   N540ES