Okay, no problem, he got a timberboard panel, and eventually i got round to making it, we screwed and glued 3 battens on the underside, from memory, they were 18x69, running virtually full width, 600mm iirc.
He mentioned today that it has warped somewhat. A rough guess, about 20mm up in the middle with the two sides down. Although i havnt seen it yet.
I have never had a problem with them before once reinforced

I wondered about pulling off the wood and clamping it back slowly whilst keeping it indoors to dry out a little more. Then replace with new pieces underneath?
Either that, or i fold up a metal top hat section and screw it back to that.
Thoughts?