Hi Tony,
I have finally found the culprit causing the plastic burning smell.
It was nothing to do with the vehicle itself, but was caused by the DC-DC charger mounted in the rear on the cargo barrier.
The input terminals had melted. I could not see them due to the charger being mounted low down near the floor.
Anyway, I assume one or both terminals maybe worked loose and had a high resistance connection, thus heating and consequently causing the burning plastic smell.
Problem solved, removed the terminals and hard wired straight onto the circuit board with an Anderson plug.
Found it purely by chance, noticed a piece of melted plastic on the floor under the charger!!!!
Regards
Rob