I think he is talking about dimpling the skin, not the fiberglass.
This is how I did it:
Do not dimple the tip attaching holes for now. When your VS is riveted up,
install the fiberglass tip, drilling through the holes. Attach with 3/32 clecos. When you are satisfied with the fit(maybe you will need to sand, fill), then
drill to final size, dimple the VS skin and countersink the fiberglass.
Attach with CS-4 rivets.
I glued a strip of .032 sheet, half inch wide, on the inside edges of the FG tips, so the CS-4 grab the aluminium, not the soft FG. It works great.
If you dimple now those holes, the dimples will interfere with the fitting of the FG tip.
Yes, drill size is #30.
Hope this helps you.
oceanbird
VAF dues paid