It is almost like primer wars, to prime or not, what kind of primer. There are dozens of ways. The post above kind of ststatus quo. The old sage advice build it per plans.
The simple, lightest, easiest to install are the pins wVan's sells with the tabs (as shown above). External (ever so slightly) and one screw and nut plate. Done. When taking off one screw, pull pin out. The fancy recessed covers come in all flavors, but tend to be way more involved, costly, weighs more, time consuming to fabricate and in use more time to remove. If not harder to remove and install you end up with more extra loose parts. HOWEVER Viva La difference, different strokes.... what ever makes you happy.
On my RV-4 I had a slot or notch in top and bottom cowl to make room to pus the pin home. There was no positive retention and in 1000 hrs plus never migrated out. On my next build:
Cowl Pin with Welded Tab
store.vansaircraft.com
Cowl Pin with Welded Tab
store.vansaircraft.com
PS: Out of the box (but has been +35 yrs) is put Van's RV cowl side pins in from cockpit side. You have small hole in firewall and fed it from back to front. The pin was extra long and came out to the bulkhead under panel. There was a tube bonded into place to guide it to the piano hinge. It was a popular idea or at least an ideal, at one time. It will make the absolute cleanest looking installation. I recall people's big complaint with this approach, was to take cowl off or put back on, they had to climb into the cockpit. Also might need a 2nd person to wiggle and cajole the two cowl haves together to get pin started. Sounds like more work, but dare to be different.