On Wed, 05 Nov 2008 17:00:02 -0600, Geoff Schultz
wrote:

It's fairly obvious that the coring is soaked. How do I go about drying
this out before sealing the leak and replacing porthole?

It's a tough repair which has been discussed on "rec.boats.building"
from time to time in the past. You might be able to find some of the
old threads by searching Goole Groups.

Basically the core is damaged beyond repair where it has gotten wet.
As others have said there are three basic methods:

1. Remove the top skin, replace/relaminate the core, replace the top
skin.

2. Remove the bottom skin, repeat as above.

3. Drill a series of holes, dry with heat and/or a vacuum pump, fill
holes with thickened epoxy, perform cosmetic fix on drill holes.

Method 2 requires working from below which is difficult but may be
easier cosmetically if the repair can be covered by the head liner.

Method 3 is relatively quick and easy but long term integreity is
suspect and the holes can be difficult to cover. The extent of core
damage can be determined by examining the drilling residue.

Method 1 is scary but probably yields the best long term out come.
Some people have reported success making a thin cut around the
perimeter of the repair using something like a Fein Multimaster to
make the cut; lifting off the outer skin intact; and then replacing it
at the end, leaving only the cut line to be patched up cosmetically.
One difficulty is predetermining the extent of the core damage.