CMP round roof hatch padding?

[Grant Bowker]

It was installed in 3 sections around the ring.
The padding, along with a curved backing plate (mine looks 3/32" when heavily painted) with 2 caged nuts on the inner face of each plate for securing to the ring is wrapped with canvas (in 3 parts (upper, lower, face - curved to fit the ring). As far as I can tell, the canvas was only secured by being pinched between the plate and the ring.
I want to go and fabricate parts for the 15 cwt trailer but will try to post photos later.