I really love the idea of putting in smaller seats to maximize the small cabin space. I saw, on here, a guy stationed in HI that built a frame for two collapsible boat seats in the rear. The were a tumble style like in minivans that could be removed by hand with a pin. I have a newborn that I have her booster seat attached using the Latch system to mounts on the frame. When she gets bigger I want to install a collapsible seat behind the driver seat. Have you made any progress in your design? The HI guy's design was on a frame that went all the way across the tub. I know ppl that put boat seats in the front need to raise them off from the frame and sometimes use pucks. I wonder if mounting a boat seat to a front passenger frame without a riser would be the right height. This would obviously allow it to tumble forward providing more room when not in use, but the exposed frame is bulky.