Floor units first:
400 cm wide base unit with door via Ikea. But shortened to 450/500 cm deep. To offer a little more working room at the back of the van. As we opted for a wider kitchen unit on nearside this time. Mainly to give better work surface area.
Reposition the electrics panel over to rear by 200 cm.
I looking at building a custom cabinet on the end of the 400 unit but it's possible a standard IKEA one will do the job ( I need to enclose the porta potti if possible).