Turns out washing down your trailer isn't a waste of time. I have wondered. I HATE doing it and it takes so much time to do properly that I won't take the boat out for short trips. Just got the first WOF after three years from new and the mechanic said there aren't any signs of corrosion. He thought that was unusual. Trailer is stock standard galvanised, although I did treat it with some products prior to first use.