-- Last Updated: Nov-26-12 11:36 PM EST --
My rowboats have wood gunwales. I ought to oil them more often than I do, but I do occasionally go the extra mile to get oil onto the hidden contact surfaces between wood pieces. The central one-third of each boat has three-layer gunwales, with the innermost layer being a slotted section. The other two sections are a standard inwale and outwale which run the length of the boat and sandwich the hull (hull is hidden from view, as seen from the top). I can remove the slotted inwale from the central one-third of the boat easily enough, but even though I hardly ever do so, the oil finish on the hidden contact surfaces stay pretty good even after long periods of neglect. I apply the oil pretty heavily there, and it's an ugly mess when exposed at the next disassembly a few years later, but it's quite well bonded to the wood and quite water repellant. The main gunwales really can't be disassembled all the way since the inwales are glued along the decks (the outwales can be removed, but I've never done it), but since I always hear about screw locations rotting before any other location, I occasionally remove the screws (just a few at a time so as to avoid any re-installation complications) and dribble oil into the holes. I'm careful not to cut any "new threads" when reinstalling the screws because then the whole job would do more harm than good in the long run. I suspect that the thick coating of oil in the screw holes is just as long-lasting as what I see when I remove the slotted inwales, so I'm sure it works pretty well. So far, there's no trace of degradation from moisture.
I think that more important than coating every hidden surface with oil is how the boat is stored and how quickly it dries after being soaked. I'm lucky in that I'm able to insure that everything dries quickly and thoroughly once I return home after a trip, but not everyone has that option. On that note, one thing I do is that once the boat is upside-down on the rack, I reach into the stems and mop up all the excess water that's run there along the gunwales. No point in giving it time to soak in, especially with so much end grain being available in there. Also, it's a good place to really goop in the oil too. No one can see if it looks bad in there.