Rich, along the idea of Dale's drawing,
just something you could have made locally.
and as for your thought on the board, I did that on my 14' Crestliner trailer.
no rollers, just float the boat on and nose it into the keeper at the winch and
it sort of loads itself. I don't know if your boat would be too heavy to eliminate
the back rollers or not. The underneath roller just sort of guides the boat straight
onto the trailer. I guess it is a matter of choice of how you want to address the issue.
When I use the Crestliner, I don't back all the way into the water to put the boat back
on the trailer . . . . but, I do get my feet wet getting on the board at my ramp.
and, it can be a bit hazardous if you are off balance a little with your footing.
The board does not have a groove . . . it is a P/T 2x12 with P/T 1x2" strips for the
boat keel . . . then, carpet glued and stapled to it. This is about 6 years old now.
the PVC side guides do a 90% good job of getting it straight.
I also put a bead of grease down the keel keeper for easy slide on/off.