OK here is what i have done.
Seems to work pretty well ive done 100 miles on it and taken it up to 80mph.
They are on all four wheels now.
The hose clamps seem to centre the bracket plate like a chuck to keep it central. Maybe the centre cap helps centralize too?
I've not had the wheels ballanced yet but will do this in time.
There is decent clearance between the hoze clamps and the disc brake ~10mm.
The bolts screw into aluminium
rivnuts which i have "riveted" on to the bracket plate using a vice and socket set.
I used a 800w drill to do up the hose clamps nice and tight. Push the back in as you're doing them up and afterwards hammer the hose clips flat against the wheel. The hose clip forms a square around the perimeter of the spoke.
The backing sheet is held really firmly by the hose clamps. I used sticky white foam inbetween the wheel and bracket (optional).
The moondiscs unfortunatly have a slight gap between them and the wheel, but this is barely noticable, about 6mm. This is the thickness taken up by the hose clamps and bracket. Buy hose clamps with a short barrel, compared to your spokes, else they stick out past the bracket plate.
Its all aluminium or stainless steel so it shouldn't rust.
I used special bolts on the moondisc to prevent theft/vandals.
The discs are lightweight only 300g.
The brackets were made my lasermaster from a CAD drawing i sent them. From 1.5mm aluminium. I will post the CAD file upon request but it is specific to fit nissan leaf wheels.
The discs are pizza lids from ebay 0.8mm thick aluminium.
The secret to getting them shinney circles is to spin them and rub them with a brillo pad.
I used an angle grinder bolted to a work bench and a 12v power supply to slow the speed to a safe level (spins dangerously fast at 240v). Centre drill with a 22mm hole cutter.
You have to spray the moondiscs with clear laqour to stop them going gray.
all in cost me about £100 most of which was the cost of the laser cut brackets.