From Our Guru, Tim Lackey...
Tim Lackey had this to say when I emailed him. It pretty much takes care of my question:
The sides of the cabin trunk are not truly hollow. What you have is a solid structural laminate, running from somewhere in the rounded curve at the top edge (where it transitions to the coachroof) down to the sidedeck level. There is an interior liner made of very thin and flimsy fiberglass that has no structural relevance at all; it is for appearance only. There is generally a variable amount of space between the two, which may lead to the impression that it is hollow. Generally, it's not necessary to do anything to the cabin sides, but if you have severe movment as a result of a horribly deteriorated coachroof, you may need to perform repairs.
The exact situation you have, coupled with your skills and what sort of access you can gain to the area from inside or out, will dictate your repair method. If you needed to repair the sides of the trunk, it would be easy, but you might have to compromise the interior liner to gain proper access. That's the problem with molded liners: they block access for the repairs that most boats eventually need. I think it would be too much work for dubious gain to try and open and then patch the liner, which is no great shakes to begin with, so if you did need to go this route, I'd suggest considering some other sort of interior covering that pleased your sense of aesthetics.
Recoring is messy and time-consuming, but is not technically difficult. Just remember that the whole point is to bond the new core WELL to both bottom and top skins (that is, no voids and firmly affixed), and to prevent the possibility of any water getting into the core again, even with a non-organic core material. Solid laminate in way of deck hardware and openings, and around all fastener locations is the best way to go. At a minimum, be sure to overbore and refill (with epoxy) boltholes when installing hardware. The hardest part of the job is creating the fair and smooth surface at the end that you need for a fine finish.
Good luck! It's a great learning process.
Tim