Many thanks for your reply, Rojie .
With all the rear seats removed I think I should be able to set up a desk, 2 monitors and an office chair.
I don't need to stand up but I estimate a minimum internal height of 137cm is required to allow me to sit comfortably (if anyone could tell me what the floor to headlining height is I'd be very grateful).
Power consumption of 2 monitors and a laptop I estimate to be about 350w, so I think a leisure battery with an inverter should do the job?
Any other guidance would be welcome.
Many thanks,
Simon