try these.
My trailer is 100% bunks, no rollers. the few points I can share are these:
1. Provide a support for the keel to rest on during transport.
2. It is nice to have the boat sitting a little higher, like 2-3 inches or so, such that the keel will swing down to rest on its support, exposing the cable and attachment point. It makes for super-easy inspection and replacement of the cable when necessary. just remember NOT to transport with teh keel fully retracted! It is hard on the boat.
3. While I do not have one, a wide bow roller or other support forward will help lift the boat into a proper angle in line with the trailer while launching and retrieving. The rotation of the boat on the trailer when pulling out at a steep ramp is substantial. Your bow eye moves a lot with respect to the trailer without some sort of forward support.