This comes as 2 bags, one for each side, intended to be mounted by your thighs. You glue in fastlock clips and the bag clips in/out easily. Has a Velcro flap you could put the rudder cable through.
I mounted one bag behind my seat (not enough room at the thighs). It has worked great there, it clips in/out quickly and securely and the double zipper works well enough I can zip open/close with either arm/side. Very well made (all Northwater products I've seen are). Can't comment on it if mounted at the thigh.
Minor nit: I think it would work better with some kind of hard shell to keep it's shape.