As I said in my original posting, it could be the Seitz windows that DVLA recognised as 'motor caravan' as these and different graphics are about the only differences between my conversion and Otterspotter's conversion? I also deliberately took plenty of photos (from angles to clearly show solar panels, rooflights and TV aerial) and stuck labels (using the exact DVLA wording) on them to show the requirements listed by DVLA?..
Found it - on this forum
Woohoo, got one!
Must be my lucky day, got my V5 back with 'Motor caravan' body type! Had to add more graphics than I wanted (but pleased with result anyway). Sent 22 photos in, with description on the back and labels on the front showing exact wording of DVLA requirements i.e. 'motor caravan style graphics'...www.motorhomefun.co.uk