I installed the two elevators' end caps. First I noted the space available in the elevator's metal flange, and measured how much flange I must sand off of the end cap for it to fit into the elevator. I marked this line with a red marker, then sanded the fiberglass flange down with my belt sander. This works well as I can really control the line.
Next, I fitted the cap into the elevator, made any last corrections, then matchdrilled using the existing holes in the elevator. With holes drilled, I deburred and dimpled the elevator holes for CS4-4 pop rivets, and countersunk the cap holes to accept the metal dimple.