One thing not mentioned when it comes to lightning is that if you are at the dock and are plugged in none of this matters. Just because your mast may become a lighning target does not make it the only targety. A neighbor last week has good lightning protection and grounding on his boat but when a tree nearby was hit it inducted the electric wires. In the process he lost everything electronic in his house as well as every bit of electronics plus the A/C unit in his boat. Insurance estimates are already over $5K in damage.
Your shore power cord is a very problematic connection. Most docks are not surge protected even if well grounded. When your AC power lines are inducted your grounding plate won''t save you from the surge through the shorepower line. Only a heavy duty surge protector will help you then.
Considering many people are at the dock when a storm comes consaider twice before leaving your boat plugged in all the time when you are away.