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Tom - Thanks!
After looking at it some more, I decided fill the gap around the tube with foam insulation - the tube had no support in the hull and the condition of the gelcoat and fiberglass at the entry/exit points was pretty rough for a good seal.

I ground off the gelcoat on both sides and wrapped the replacement tube in waxed paper and inserted into the hull

[img]http://home.comcast.net/~art.odea/images/WC2A0859.jpg[/img]

Making sure to use lots of masking tape around the drain hole inside the boat, I injected a foam insulation (I used the Lowe's equivalent to GreatStuff - a product from Dow) and let it expand and cure. I realize the foam is not the preferred material to use, but I think I read that its use as a structural filler, like under the deck, is not recommended. It expands and flows everywhere, and the stuff is impossible to remove if it goes where you don't want it to go. Here's the inside after removing the excess foam and masking tape:

http://home.comcast.net/~art.odea/ima...2A0858.jpg

I then filled the hole with West Marine Structural Filler, and brushed on gelcoat (not taking the time to match the color...).
Then I used a dremel tool to restore the hole diameter:

http://home.comcast.net/~art.odea/ima...2A0862.jpg

Next, inserted the tube that was flared on the stern end and cut to length...

http://home.comcast.net/~art.odea/ima...2A0866.jpg

Filled everything with lots of 5200 and hammered it home using an air hammer with the flaring tool:

http://home.comcast.net/~art.odea/ima...2A0874.jpg

It's now tight and dry as a bone.
- Art