Guys, here are the basic issues you have to worry about when keeping your boat in the water at a dock or marina:
1. Keeping it floating. Water can come from above as well as from below. Will it be protected from rain via a roof (covered slip) or just the mooring cover? Rain can also blow in sideways, so an automatic bilge pump, perhaps even two, tested regularly, with a dedicated battery and potentially a high water alarm. Will there be a source of electricity to keep the battery charged and the pumps working? A hard working bilge pump can deplete a battery in a matter of a hours. A drive on dock or boat lift eliminates these issues.
2. Galvanic corrosion. If the dock is powered, there is often stray current in the water and it will eat the least noble metal it can find. Consider adding a zinc anode to the hull in addition to the one that is on the motor.
3. Marine growth. Even in freshwater, slime buildup can be substantial. If you can pull the boat to clean it a few times a season, you might be able to make do, otherwise, you may need to consider bottom paint.
4. Security. How will your gear be secured? Locked on board? Stowed seperately? Is there any security presence at the marina like a guard shack? Also consider what your insurance will cover if someone does target your boat.
Scared yet? Don't be. These are all issues that can be managed. Arriving at a marina, stepping on your boat, turning the key and taking off can be a very liberating experience. Well worth it if you've got the coin.