Slimy Grimy is "okay" ..... and not as harsh to the environment and people using it ..................
BUT
From my personal experience "On & Off" is the best and I have used both.
On & Off is an "acid" so precautions MUST be taken -- I use kitchen rubber gloves and make damn sure that I stay up-wind of it (the outgassing is horrible) --- but it is as simple as spray it on- wait a few minutes - and use a soft car brush on a pole to rub off, rinse with hose - done !
I also rarely dilute it to the labels recommendations -- thus leaving it a little more "potent"
https://www.amazon.com/Star-EZ-OFF-B...f+boat+cleaner
As for cleaning where the bunk rails are (or rollers) I would relaunch and deliberately take the boat out on the trailer askew of normal position. I recognize that this requires having a ramp handy as you certainly do not want to travel any distance with the boat on angle in the trailer--- I happen to be one of those lucky ones
.