Does your rim have eyelets? If not, with the rim strip off, check for any tiny burrs around the spoke holes left over from when they were drilled. Run a round file around the rims to smooth off all the spoke holes and follow with fine emery cloth. Then replace with a Velox cloth rim strip. This stopped repetitive punctures we were getting on a new Velocity Deep V rim on the tandem (125 psi.)

Also make sure that you don't have any over-long spokes protruding so far above the nipple heads that they reach the rim strip when it is forced into the spoke hole by the air pressure.

For rims without eyelets, I've built two wheels with the little plastic plugs that Velocity makes for their non-eyeletted rims. They would protect the tube from burrs. But I'm still partial to rim strips, so far.