Chip,

It might be easier (for an experiment) to just make a Nick Schade type seat back which can move more or less forward and to have a seat bottom of foam which is held to the hull with velcro. This will allow placing the seat bottom at different postions to find the best location to balance between weather and lee cocking of the boat.

If you do choose rails, I believe that two rails would be a *much* stronger way of spreading and supporting your weight. They each could have a lot less vertical bulk and get your weight down further than the central rail.

Rick