Rodger, it is cristal clear that working from the inside through a port is the most obvious solution.

But try to think (literally) more out of the box.

We have on the beach where I sail in summertime swimming lines to keep the swimmers away from the breakwaters. About 6 years ago, I sailed with an old P15 by accident over one of these lines . The line got stuck between the transom and the rudderblade of one of the hulls. I was pushed by a wave and the transom teared off. Within 20 seconds my hull was completely filled with water.

So, problems to return to the beach with a limp cat, not to mention the difficulty to pull the cat single-handed on the beach again.

It was in the middle of the season, I had no time for an extended repair. I just pushed everything back and laminated over the transom till 5 inches overlap on the sides.
It was rocksolid (though not a beauty solution).

That gave me, amongst other reasons, the confidence for my momentary cat which has no interior at all. The hulls are massif and filled with foam.

So every possible repair has to be done from the outside.