I've done about 5 sets of trim tabs.
My steps are.
Predrill
Put all of the screws half way without the tabs to make sure its not going to chip anything out.
Remove screws and squirt 4200 into the holes. Leave a blob on the outside (this will basically turn into a gasket when you tighten everything).
Cover the screw threads with 4200. WEAR GLOVES
Then install you tabs with the gooped up screws.
Then clean off as much extra 4200 as you desire.
Personally, if you use 5200 its going to rip gelcoat right off if you have to uninstall the tabs at some point. But thats an age old debate.