They seem to have been doing the job correctly on the fuselage:



What worries me a bit more is this:



The backgrouond shows the wing of the A-4 with a honeycomb main spar.

James, you need to use the previous technique for the main spars ( wings, rudder, stabilizers ). A good balsa fiber spar with vertical grain and carbon fiber layup will do the trick and be probably only 10 grs heavier and also cheaper.
Also I am not convinced by the point hinges honeycomb reinforcement blocks.