Simple, get a Hobie on Steroids like a Stiletto 27
. A little harder to trailer though.
On the porta potty thing. You would only need the top half of the unit. You are sitting in water if you need for flushing. Mount it in front of the beam like the Kat Kooler brackets, a big beach towel will work for the privacy curtain. Or she can sit on the tramp and pee thru the lacing. Bathing suit aside, pee, then the built in bidet (?sp) does the rest. Beach towel works here too.
JMO
Clayton
S27, H16