https://cimg5.ibsrv.net/gimg/www.off...6c8da731e8.jpg

Tape up both sides of the holes. the holes get filled from the inside with a syringe poked thru the tape and soak for about 10 minutes.
it's overkill but peace of mind i guess.

your transom is already cut right ? your other thread sounds like a bilge and transom assembly freshen up
I removed the tiller and didn't need to cut the notches for it.