Looks good. So much space you could turn it into cube storage. Any photos of the brackets?
I have fixed a small bracket, near to the top, either side of the footwell pockets for support at each end (4 in total).
For the centre support I have utilised the heater flap hinge screws to fix the brackets to. The underside of the shelf is
just above the knob for opening the heater flap and remains easily accessible .
Pic 1 shows an end support, Pic 2 is the heater flap hinge screw.