OK, mine has square tube between the top and bottom of the front and rear beams, the rear inners from the bottom of the beam only and is accessible with a Stanley screwdriver + ring spanner, this allows for a full width traveller plus the outer rear bolt heads+ rubber stop limit how far the traveller can run. Everyone has their own take on how the beams should be mounted, I like the idea of countersunk allen heads flush with the top beams into captive nuts in the hulls,
Cheers,
Roy