Since your trailer is steel, take some extra time to soap it down/rinse. That would be most important in my opinon.
In all honesty, if you really want to go the extra mile go buy some Salt-away but if not don't worry about it and just flush the engines with fresh water when you're all done. Furthermore, when you get home take the boat out for a short spin on the lake, that'll take care of the rest.
I wouldn't be overly concerned.:driving: