My two CENTS!
Do not run the plywood down around the drain whether it is a tube or screw plug, 90+% of transom rot starts at the drain plug.
My glass work was done by one of the finest guys on the east coast, he was at the time head glass man for Hustler. He told me the two most important things to stop water migration was no wood by the lug and to isolate the stringer wood from the transom wood. The transom wood on mine was cut straight across, there is no structual reason to run it down into the vee. The area below the ply in my transom was built to 3/4" solid glass, he said it will never go bad. He did the glass work to with stand way more ponies then I will ever put back there, note the doubled stringers and extra gussets there is even more forward no doubt one of the strongest 22's out there.
No matter what your beliefs are "GOD BLESS AMERICA"
Fully retired marine tech near 60 years in the biz.