Now that the entire board has been stripped, it’s time to fair the deck and hull and shape the rails. “To fair” is defined as “to make the connection or junction of (surfaces) smooth and even.” Because we milled the strips ourselves, there was some unevenness in the thickness of the strips that needed to be evened out. A block plane or spokeshave works well for this but be sure to set it for a very shallow cut because they can be too aggressive and tear a chunk out of the strips. I like to use a random orbital sander with 80 grit sandpaper even out most irregularities and fair the deck and hull. If you keep the ROS moving and change the sandpaper before it gets dull the ROS will knock down only the high points. It will probably take a couple hours to sand the deck alone, so get comfortable. Take your time -- this is where you release the true beauty of your woodwork! I always say it's OK to buy cheap tools but never skimp on the sandpaper! And at the very least wear a dust mask. Even better, a respirator. Some people develop severe allergies to red cedar dust.
A word on workspaces: don’t ever think that you could complete a project like this inside your home or apartment or within any living space. The sanding, fiberglass, and epoxy work is just too toxic. Sanding should be done outside of a living space and even away from where you plan to do your final varnishing. I prefer to sand outside, in a driveway. I even close the door to my garage workshop to keep the dust from flying inside it. You might find that it’s a great way to meet your neighbors as they stop by to ask what you are building and compliment you on your beautiful woodwork.
I found that a rasp works best for shaping the corners between the rails and the hull and deck. The end grain doesn’t cut easily with a block plane -- the red cedar is brittle and tends to tear. We drew a pencil line about an inch below the top and bottom of the rail and used it as a guide for rounding the corner of the rail. After initial shaping with the rasp, we sanded the corners by hand.
After the entire board has been sanded with 80 grit paper, we sanded it again with 120 grit. Since the purpose of sanding with 120 grit is only to smooth out the scratches from the 80 grit paper and not to fair the board, it takes a lot less time. I don't think there is really any reason to go finer than 120 grit. Several coats of epoxy and varnish with smooth it out plenty.