Well just a dumb question. My buddy just bought a 2000 F350 to tow the Cig T/G . The thing is that he got a deal on it and its a manual trans. Does any aftermarket make and aux e E-brake kit so i don't have to worry about it sliding down the launch ramp. I was thinking along the lines of a disk brake to go on the drive shaft like on heavy equipment, Or I was thinking of putting on a line lock like on my race car.
What are your thoughts?

Use the manual parking brake, and make sure its in good shape. With a truck of that age, and given your area, I'd probably replace all of the components due to salt deterioration.

When parked on the ramp, just turn off the truck, and leave it in first gear. When you are beginning to pull up the ramp, leave the parking brake engaged, and build clutch pressure against the brake (slightly). Then release the brake. If you build too much torque against the emergency brake, and then release it, you will spin the rear tires. Is the truck a 4x4? For the just mentioned reason, I would ALWAYS engage 4x4 when pulling the boat out of the water.

The line lock is a good idea; but I don't know how well it would last on a street driven vehicle.

micro lock makes a manual and a electric brake locks for wreckers. line locks have a short on period and will fail. the micro lock will do all the brakes.