RE: applying koverall with WBPU
I agree (for whatever that might be worth) that primer is needed on solid surfaces, i.e. sheeted wings, plank fuses, cowls, etc. Lately i have been using rattle can grey Krylon. It dries fast and sands great. Then on to the HD exterior latex. I am in the finishing process now on the first plane i have used latex and so far so good.