Just hold it up to the boat, and mark the area to install carefully. The ladder itself will act as the template, because you hold hte lower pads flush. Where they fit at allow a tad of room, as the top will go down slightly when the studs insert.
Use masking tape on the deck to keep from star crazing the area, and use silicone on the mount up for sealant.
Use the Tony Stewart method from TV, Measure twice (3 or 4 times) drill once!
Good luck!
Tough to drill on your toys~ Isn’t it!
BCB