There is a product on the market refered to as a "myers hub" or possibly a sealing type locknut
check this site out also http://www.electrician.com/articles/myers.htm http://www.electricaldeals.com/html/search.php3?column=AllenNum&search=MYER&source=ovr
this site has an illistration of a hub
If you install two one on the meter and the other at the panel I don't see a proble interconnecting with PVC (two male adapters and a nipple to fit)
312.2 Damp, Wet, or Hazardous (Classified) Locations.
(A) Damp and Wet Locations. In damp or wet locations, surface-type enclosures within the scope of this article shall be placed or equipped so as to prevent moisture or water from entering and accumulating within the cabinet or cutout box, and shall be mounted so there is at least 6 mm (¼ in.) airspace between the enclosure and the wall or other supporting surface. Enclosures installed in wet locations shall be weatherproof.
Exception: Nonmetallic enclosures shall be permitted to be installed without the airspace on a concrete, masonry, tile, or similar surface.