Garboard plug instal
 

Why am I snapping screws after pre drilling these holes. It has happened twice now. Been using brass plug and hardware. Should I go with stainless plug and hardware? Maybe I'm hitting some hull and deck putty during install. Any thoughts?

Drill, tap, and use machine screws.

Do you mean the screws that hold the garboard assembly to the transom?
I predrilled the holes and used frearson head silicon bronze screws to mount the assembly to the transom.Worked fine in my case.
If you don't drill the pilot holes large enough,it's easy to break the screws or ruin the heads of them trying to get them in.

I probably went "overboard" with the installation.I overdrilled all the pilot holes,and even the large hole for the drain.
I gave them a good coat of epoxy,followed by a thickened mix of resin and after it cured,I redrilled the holes to the size needed applied a ample amount of 5200 and installed the drain.

I think bronze is a better pick over the stainless,especially for saltwater use in its higher resistence to electrolysis.

Those are the screws I'm talking about. I coated the large hole with epoxy before installing the drain. I did some research and most everyone recommends pre drilling which I did, but also using the same size stainless screws first to create the threads then back them out and screw in the brass ones. I did this today in 5 minutes successfully. Wish I knew this before 2 previous install attempts.