
I've also had a reply from Steve at Dormobile, who confirms there should be a 'half-moon' shaped bar glassed in across the hinges and halfway across the front AND back.
I think they have possibly changed the design over the years, perhaps adding the strengthening bars to later models, hence the differences

Oh, and further probing shows that the plates reinforcing the hinges were probably welded to the bar, which makes sense to me.
It looks like I'll be cutting out and fibreglassing in new bars and plates on mine - oh the joys of bits of fibreglass in your fingers and hands, and sticky resin everywhere - brings back memories

Cheers,
Robin.