I purchased some black plastic end-plugs that fit the RV-12 step ends perfectly. See my old VAF forum entry below:
If you want to fill those somewhat unsightly tooling holes on your RV-12's wing tip bows and stab end ribs, you might want to use the following finishing caps:
-- Hillman Arrow Clips - Nylon (White) #394150-C (for the 3/16" holes)
-- Hillman Arrow Clips - Nylon (White) #394148-A (for the 1/8" holes)
I found the above clips at my local ACE Hardware store.
To seal-up the ends of the foot steps, I used the following plastic end-plugs:
-- Hillman Round Cap Plugs (Black) 3/4"
I found these end-plugs at LOWE's.