I like to turn the boat over with the bottom up. Place the bottom on it and mark where the ribs will be , take the bottom off and epoxy saturate that marked area where the bottom and ribs will meet. Same at the ends
Then place the bottom back on the boat. Drill two holes at the ribs and attach the bottom with small screws to each rib , along with the end pieces.
Now turn the boat back over and run a bead of epoxy along the sides and both sides of the ribs. After the epoxy has cured then trim off the excess part of the bottom sticking out from the sides. Now run a fillet along the inside of the boat , including the ribs and get ready to glass the boat.