Rotten wood around portlights?

[Lazy Jack 32]

I started replacing a portlight on the Lazy Jack schooner (vintage 1977) and found the plywood between the fiberglass outer cabin side and the plastic veneer on the inside cabin wall was mushy and wet. First thought was to remove the portlight and soak penetrating epoxy into the exposed wood (the rot is mostly below and to the sides of the portlight), but descriptions I found on-line of penetrating epoxy say the wood must be totally dry first before the epoxy will soak in. So the next plan would be to remove the portlight, and cut away a generous portion of the inside veneer to let the rotten plywood dry until next spring before treating it with penetrating epoxy. I have an oscillating Dremel saw and am ready to operate, but thought I would check with this community to see if anyone had done this before. Is there an alternative to cutting away the veneer? There are two portlights for sure that show signs of rotten core around them.

Any advice will be appreciated.

Charlie