I think the intermediate frame is as valid as any other idea, and will let you use shorter/thinner seat slats. A couple of ribs fastened to the inside of the gunwales, passing under the seat slats to support them, might be an interesting approach. Depending on the width and depth of the hull, and its stability characteristics, raising the COG by 1/2" or 3/4" may not adversely affect its handling enough to worry. If you are building narrow, tippy hulls, that won't be a good idea unless your customers are accustomed to paddling such craft!

As for padding, maybe you can glue foam sheet to the top of the slats?

I like to use a sheet of closed-cell foam (like a yoga or exercise mat, some like to use the waffle-textured camping sleep pads) that runs from the foot rest to the back of the coaming. The sheet of foam is usually long enough so that it can either be doubled over where you sit on it, or rolled up and stuffed at the back of the coaming to act as a back rest and sacral support. Do note that the foam pad may interfere with wet-exits and re-entry if its too loose and floats once the hull has water inside.

: One idea I am tossing around is shortening up the floor by adding an
: intermediate frame. Cut it off at the top stinger and space it 18 to
: 24" forward of the one at the rear of the coaming. (Just guessing at
: the distance) Just long enough to put in a seat and a tight rest if
: someone wanted them. Then you just need a short board or slats and you can
: still keep it low to keep the CG low.

: I am about to start a new boat this afternoon we have been design for a
: couple of months now. Once I get the frames in place I am going to spend a
: little time looking into floor board options but I am leaning toward the
: extra frame.

: I think your probably right that glassing the floor boards would work. I have
: some interest in building a couple boats for others, so I am looking for
: something that is not to labor intensive or costly. And I am going on the
: assumption that most people are not going to want to sit on a hard wooden
: floor, so it's going to need a padded seat in it.