1. Check that you won't be drilling into speaker wires, control cables, hoses, foam flotation, or conduits under the gunwales. Drill the aft holes of the rear bases first. Using the bases as guides, drill the front holes.
2. Bolt the bases in place with the supplied rubber gaskets and backing plates. Use silicone sealant on the deck. Tighten until the gaskets start to compress. Check that the bases don't wiggle, and then take an extra quarter turn. Avoid power tools or over-tightening, which can crack the gel coat and fiberglass.
3. Secure the rear arch to its bases, attach the front legs to the arch and adjust them to where you want them to contact the hull. Check that each base is in the same location fore and aft. As above, mark, drill, and install the forward bases. Attach the forward legs.
4. Before a final tightening, center the tower by taking diagonal measurements. Shift the tower until measurements are identical, torque down the fasteners, and put in set screws. Give it a good shake. Don't use the tower if it moves or rattles. If secure, re-torque after a few uses.
Where's the Beef?
The manufacturer says if the bases are to be mounted on fiberglass less than 3/8" thick (not counting the gel coat), you'll need a backing block. We say, do it anyway. Use 1/4" or thicker composite or rot-resistant plywood. Cut as big a piece as possible to spread the load over the greatest surface area. Taper the edges to ease the localized stress.
Drilling the Perfect Hole
To avoid chipping the gel coat, or starting spider web cracking, run your drill in reverse. This will prevent the bit from "biting" into the gel coat and chipping it before the bit reaches the fiberglass beneath. Drill a 1/8" hole first as a pilot hole, and then follow up with the larger drill bit. To properly finish the hole, chamfer the edge to a 45-degree angle with a small round file or sandpaper.