Mick Pearce made this simple modification to help center the boat on the trailer and aid recovery.
The modification is simply a couple of small plastic wheels mounted on the rear of the main spar which guide the hull onto the central rollers.
A slightly modified recovery technique is required.
From a gently sloping surface like a beach the trick is to tilt the trailer up at the hitch end after hooking on the winch hawser, then merely winching in centralises the boat. The boat is both pulled onto the trailer and the trailer is pulled under the boat, then hitch on car and away.
On a slipway, using the car, I just dip the guiding wheels in
the water float the nose of the boat between the guide wheels then winch in. A
bit more of an effort is required because you are winching up a slope, as it
were, but it works every time.