Yeah that was my biggest concern with the mounts, will they support something of that design as i know they do create quite a bit of force and the one thing i thought about with having a 12 sided bar (i think it is 12) is i don't understand having that many sides when less sides would be more efficient say 8 or so while still maintaining a rounder shape than a square tube. At least that is my thought and while i am an army engineer and could design the hell out of it in CAd, i am by no means an expert in this application so i can only hope Hobie did the testing with many styles before saying that the 12 is strongest. I think of it like using a wrench, more smaller flat edges equal the easier stripping of said edges and in this case using a plastic "nut" that kinda seems like it would greaten the chance of stripping the mount out if too much weight is applied. Sure would be nice to know the manufacturer suggested load bearing weight limit.
I do like the idea of using two tho. will spread that load out more.
The other thing i was wondering will the arm fit under the hrail so it could be mount on one of those scotty swivel mounts? they seem to sit prety high on those mounts so might be able to add a cutting board or two under it to get it to swing out under the rail. I am throwing darts in the dark as i have neither device in front of me but i do enjoy brainstorming the problems!