Another boat question

Hard to believe the transom is hollow
I know right? I was thinking wood or something. Nope, one piece of aluminum support in there like a baffle in a tank just below the lower motor mounts. That’s it!
You can always add another layer of alum if you want
If it were two new aluminum plates and sealed perfect, yes. A new plate on an old one (that’s not perfect anymore) can lead to corrosion in that space.

It’s been through a couple of tree strikes, one barrel, and one sea stack hard enough to break the skeg! Well in addition to many hours of rough water. I’ll be lucky to get another 500 hours outta her anyway.
I got the kicker, 150 and the bilge all running today!!! I run a water separator and wasn’t sure how much Stabil I actually got into the motors before taking them out last year. Good news!