Joe,
The rudder is fabric covered except for the trim tab and balance tab. Use something like Koverall and dope (or paint of choice) and don't forget the rib tapes and stitching
. Fiberglass and epoxy are not designed to span open areas and will never "tighten up". The photo is of N 314BG, an F-51D painted as "Petie 2nd", S/N 414151 and is based at Creve Coeur Airport near St. Louis. I was trying to get a shot of the fin offset, but you can see the trim tab in the fore ground and the rib stitching and tape on the rudder. P2 is the port side, P3 is th starboard side. P4 is the same as P1 but with out flash and you can see the edges of the "pinked" tapes better. The pictures also show how colors can be affected by the type of lighting, flash, sunlight, shadow, and indirect.