i have just tried to take photos but camera packed up so will try to explain how it works
on the trailer the pipes conect through to a block and pipes go round from block to the preheat which is the round thing on left of photo
to convert to gas remove these extra pipes and the preheat fitting but leave pipe from rear turn off valves to front box where the conector on the right photo is conected and put the blanking plate over empty connections
the one on the left is missing its valve but the conection block is missing as well