Clive,
Is the case that the folding camper is too low down for you to see it when reversing. I have the same problem with my small 'tip' trailer that hides behind my C5.
I solved the problem by slotting in a bamboo cane vertically at front centre and rear centre of the trailer when reversing. (Temporary fixed only).
Now, although I still can't see the trailer, I can see the canes and by comparing their respective positions in my eyeline I can see which way the trailer is going. Hope the above makes sense, if not please resond and I will try again to explain