Originally that bilge was made from ply then glassed, all you have left is the glass, is it sturdy to handle, if so its probably fine. It doesn't do anything but hold water. You could try a layer of mat on the wood side if the wood is mostly gone. Be carefull it doesn't twist or warp out of shape.
I like working with cloth for joints, but I'll use mat if thats all I got,
better something than nothing.
You'll find the 90 deg joints are easier if you form a curve with putty,
cloth doesn't like sharp turns.
You're supposed to start with a narrow strip of cloth first, then lay a wider strip over that, then another wider. 3 inch, 5 inch and 8 inch strips or bigger.
That spreads the load like leaf springs.
Thats the benefit of using unwaxed poly resin, no sanding between coats, just keep mixing and slapping it on. Get the unwaxed at any boat supply store or mail order it.
I can see you left the bottom of the old transom wood with the drain tube, naughty boy.
I did the same.
I dried the wood out around the tube (heatgun) and drenched it with resin thinned out with acetone, repeated applications until it stopped soaking in, then run the cloth right over it, cut the drain tube open when it all cures.
