Kevin,

 

I'm not sure how susceptible the underneath side of the wingtip is to icing.  The NACA and the tubing end are recessed.  From photos and video I've seen of airframe icing, it doesn't extend very far back underneath the wing leading edge.  I would think a NACA fuel tank vent would be better than the tube sticking down when it comes to icing.

 

Mike Easley

Colorado Springs