In the end I went with the tactic of cutting a used piece of fibreglass to the shape of the hole and then clamping this and the mesh in the vice, using the angle grinder to cut it roughly to shape and then a small tap hammer to bend the metal aver the fibreglass.
Once it has been shaped use tie wraps (zip ties) to hold them in position.
Then add plenty of your favourite bonding adhesive. I've used SikaFlex so I doubt they will ever come off without power tool assistance.24 hours at a half decent temperature and the ties can be removed (that'll be a week then in this freezing weather).
I have also started to seal up all the holes in the bodywork. Some are easier than others (where the screen pillars come through the bodywork and the roll bar holes) but others, such as the bulkhead holes are much more difficult to access. For anyone reading this before you build one of these cars, seal these up early in the process before you put the wires though, leaving just enough room to put the wires through, then you just have to finish them off later.
