SD makes some very good points, as usual.
Working upside down in that confined space is going to be a nightmare, no two ways about it. The resulting repair is bound to be weaker due to poor adhesion and bonding because of gravity effects.
Another advantage of using epoxy is reduced fumes and vapours, esp if working in confined areas.
I understand the desire to not disturb the deck finish, that probably prompts the "inside and up" approach... but ultimately I think you'd regret it (unless, and only half joking here - you take the stick out, haul the boat and roll it over on blocks.. radical but it's a small enough boat you may get away with it with the right setup - it would also address any leaking issues you might have.)
This kind of job in our unpredictable weather is risky, but if you're prepared to wait for best possible conditions it's do-able this time of year.
Coring material is available at Fiber-Tek in Burnaby, right on Boundary road, just north of 1st Ave. They are very helpful in there too.
Once you start, there's no turning back - the boat will be unusable until the repair is completed, so be sure you need/want to do this now.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)