the way ive plugged transum holes was to glue the wood plug in first, flush with the wood on the transum. leaving the glass of the hull exposed. then grinding the edges of the glass and beveling it. then useing matting and resin to fill the rest of the hole and feathering it out over the edges of the plug. keep laying glass and resin. once it is filled (it will look ugly) then you grind it back down smooth and flush with the hull. by trying to fill with just epoxy only will give you the cracks. you need the glass to give it its strength.