Re: Islander Transom finish,varnish or paint? Or urethane ?
I/O Islander or OB?
Aluminum hull, correct?
If I/O, paint, either spar, or other finish that suits you. The epoxy has sealed the wood. The more coats of anything now all the better. The epoxy coated transom is protected from UV by being below other structure at the stern.
On an OB transom, it's exposed to UV, so it NEEDS to be covered. Use which ever product matches how you'll finish the rest of the interior. On some rigs an exposed wooden transom (final finish in spar) makes the interior really pop, on others it would look better painted to match the rest of the interior accents.
If you didn't coat all the edges when you applied the epoxy to each side (if sides are 2coats, edges would be 4), and you will still be able to get the transom to fit (on an OB there's a small 'shelf' that the transom slides down onto to support it at the bottom, on an I/O you need to make sure you don't miss the 2 1/8" targeted final transom thickness at the keyhole) and not be too tight of a fit, I'd probably coat the edges both times when you coat each side again.
When you cut the keyhole (on an I/O) make sure to treat it's edges w/ more coats then you did the edges of the transom.