I built a wooden box to put the a-cat upside down ontop of the 20 and used it to haul to the keys several times. I bought several pressure treated 2x6s, hot dipped lag bolts, and a little carpet. I made the box large enough to span the beams of the 20 fore and aft but narrow enough to be just inside the hulls on the A-cat. I cut the 2x6's to fit the N20 beams and stapled in some carpet. I then eye-balled a center of gravity and cut the length-running 2x6s to fit the a-cat beam (a-cat inverted). A little carpet on there. I then drilled four holes on each length-running 2x6 - two just under the leading and trailing edge of each upper boat beam. I then took two pieces of quarter inch line and stopper knotted each on the extreme forward and aft holes, over the beam, through the other hole, and then put a trucker hitch to tie the two together. Did that for both sides. The upper boat was really firmly connected to the rack. The rack was then secured to the trailer (notches kept the rack tied firmly to the bottom boat).

Worked like a champ...not sure how the H16 beams would interface while inverted though.