I screw the bolt down, leave it with a ring spanner attached locking it in place with a length of cord then go below, put on the nut and ratchet it tight.
A couple of links for you
Advanced navigation courses - coastal and offshore Ch7 deals with tide predictions
Tidal Height related to Pressure : Monty Mariner
The only place that the moisture can get into the cable is where the wires have been bared, so when you terminate the cable if you can seal it internally it will help.
I also wondered about that.
I also believe in check lists though in my case, as I've had the boat for over twenty years, it is a mental list that I walk through.