Three 4 meter long 15 mm square strips of red deal were ordered and these were soaked in hot water and bent to make them more pliable and then screwed to the end grain on the outer circumference of the lower ring. They were left to dry in place and then glued and screwed down again. They were then sanded down and treated like the rest of the timber with the resin/ acetone mix and wood preserver.
This provided an overhang under which to wedge the inside edges of the corner sections of marine plywood that would complete the roof enclosure. It also partly protected the end grain surface from the elements in place of the steel belt covering the ring above.
The above picture shows the ring glued and screwed to the circular beam but incidentally it also gives a good view of the under surface of the top beam showing the rail, in place over the castors and a low-profile bracket holding one of the pins transfixing the rail holding it well inside the groove.
The triangular corner roof sections fitted snugly below the overhang provided by the ring of timber.