Hi, Not sure about the weight limit for insurance here in France but most campers are certainly plated at 3.5 tonnes unless they have three axles Mine is a Hymer on a maxi chassis and is only plated at the 3.4 tonnes. I have been told that UK campers which are RHD and have the habitation door on the UK nearside cannot be reregistered in France. Being RHD is not in itself a problem when rematriculating a vehicle. If it is a Hymer I would imagine that the habitation door is located on the same side as LHD vans. Has your friend consulted any of the insurance companies or is he listening to hearsay ? He should contact the local DRIRE office and they will give him chapter and verse, They have been very helpful to me in the past. Hope this is of some help.
Regards, Tom
Toujours a Vacances !