The best thing is to take boat for a run at least once a month, and run it long enough and hard enough to get all the juices to peak temps.
But that is not always a practical option, understood.
Short runs dockside help keep the surfaces oiled, but do tend to get moisture in oil that won't get cooked out. But it would take many many dockside starts to get moisture level to a harmful point.
But the damage from a corroded cylinder or corroded valve can happen in a period of a few months.
So if you can't go for a run, I think a brief monthly run is the best non-optimal option. I don't think it is beneficial to run all the way up to temp, as what matters is oil temp and that will never get up there dockside.
What I would recommend is start up, when oil pressure gets up, rev engine a little to say 800 or 1000 to get oil slinging around. Run a few minutes, then to idle, then put in reverse. If a twin, you can put one in fwd and one in rev and that limits the strain on dock lines. Maybe a minute in gear. Then to neut, rev up to 1200 for more juice slinging, then idle, then off.
Once you do this for six months in a row, you really should do what it takes to get under way and cook the oil dry.
Also good to run boat hard on it's last trip for winter storage for boats that do that. Dry oil then for all winter.