Ask Van's
Ask Van's about this...see what they say. My money says they'll tell you to leave it alone, and I'll bet they'll cite two points:
First and foremost, clearances. Is the spar and center section designed to accommodate TENS of thousandths additional crap in between? I don't believe so. Maybe on earlier models, but not the CNC-fab'd stuff. Even a thin layer of primer is really 4x as thick when you get done with it -- one layer on each side of the spar, and of course one layer on each side of the center section (prime the anodized spar, you'd obviously carry the philosophy over and prime the center section as well, right?). Four .004" layers = .016". See if you can jam a slice of .016" aluminum in there when the wings are mated...na-ganna-da! Prime those spars, and when you go to fit your wings, boy oh boy those suckers are gonna be tight. I'll bet Van's will agree with this...leave those anodized spars alone! At a minimum, I would not mess around with the root stubs that mate with the center section. And at that point, why bother at all?
My hangarmate primed his -7A wing spars, and I'm dreading the day when I have to help him mate his wings...I predict we'll be solvent'ing the primer away. And at that point, the anodized surface has theoretically been compromised due to the self-etching primer!
The second point is -- look at quickbuild wings. Primed spars? No-sir. Anodized and left alone.
Sure, prime the exposed aluminum after countersinking, and I'm not saying you shouldn't prime adjacent mating surfaces, but the spars & center section are a different story IMHO. Just my 2 cents.
Give Van's a call if you think I'm off base here, but I recommend NOT priming your anodized spar.
)_( Dan
RV-7 N714D
http://www.rvproject.com