Here's my wiring diagram for my home-grown conversion:
Cable used is pretty much whatever the next available rating is above the fuse in that line, so from S/B to SCR (part of the Willinton kit) the cable is about 60A (from memory), from the L/B to the hook-up PSU is also 60A (or is it 70A? something like that). From the 30A Fuse to the switch panel & distribution / fuses on the right, it's 40A (ish), and the individual distribution circuits are all 10A, except the DC sockets which are 30A cable.
Ignore the "12v" breaker on the right, it's a hitch-hiker on the jpg when I exported the drawing.
I also wired in a solar panel / charge controller etc since this was drawn - connected to the 12v common in the rear fusebox (Point 'V') which is actually located in the rear of the conversion.