How are they attached - must be thru-bolts? How do you reach the underside to thread the nuts?
This is exactly what I was thinking. How on earth do you get to that to thread a bolt with a nut on the bottom side? I think that would be a great place for a track, but I'd be very worried about using it without threading a nut on the bottom side. You never know what kind of monster is going to hit your rig... especially if you go in saltwater or BTB.
Maybe someone else has threaded a nut there and can tell us how.
If you take the route LT mentioned using the YakAttack GearTrac 175 series, check first to see if you have the necessary width for the Full Back Mounting Plate. If you have the necessary width, then the Full Back actually has integrated S/S nylon locking nuts already. All you need to do is get the threads started on two of the bolts securing the GT175 on top and the rest will seat perfectly. I used this approach on my son's old Tarpon 100 in an area that was tight fit, and that mount is so strong now, you could lift and tote the kayak from that mounting point alone.
If the GT175 is too wide, you can opt for the GT90 series which is the narrower version. The smallest one offered is the one with the 3 mounting holes. There is also a backing plate for this trac as well but it is a standard backing plate where you would need to use a nut driver or a ratchet with an extension and socket to thread a locking nut on the bolt most likely due to the tight fit and the hull design.
Be mindful of any cable routing or other items like FF or electrical power wiring you migth have in the same area on your respective PAs.