A friend has recently noticed that his trailer is bent. The thinking seems to be that the boat has been bouncing and that has bent it. It is now tied down, even to go a few miles.
The other owner of Renegade had to break very hard once. The boat was only held on by the winch strap. The winch released and the boat rode up over the bow block and stopped with the bow D ring above the top of the rear screen. Aparently it looked like the RIB was trying to hump the car.
It is now tied down with a ratchet strap from the trailer to the aft rings, and fixed to the winch post at the bow.
Last summer in N Brittany I passed a Dutch combo (20 something ft motor boat) which had come to grief.
The tow car was embeded in the Armco on the central reservation, the trailer (still on the tow hitch) was in the centre lane and the boat was across the inside lane, still attached to the winch.
Tieing down, how ever you do it seems to be a good idea.