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 plugs at LOWE's. Granted, they are not "bullet-shaped" so you may lose 0.000001 knots due to flat-plate drag.
If you want to fill those somewhat unsightly tooling holes on your RV-12's wing tip bows, stab end ribs, and turnover bow, 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 these caps at my local ACE Hardware store.
David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B) - N124DH flying since March 2014 - 560+ hours (as of Oct 2017)!
through June 2018.