You are correct the regulations changed in 2018.
However if your van was previously registered as a "camping car" and you have the required documentation it can be completed via the web site
You will have to be registered as resident here and dependant on the year will depend on the documentation required, it can be a frustrating site to use as each stage requires the correct boxes being ticked and they often don't appear to be what you need.
It is possible that you will need to get a titre isole which is an inspection for single type approval, but unlikely if you can supply the documents needed.
Thank you John, that backs up some of what I've learnt and adds to it.
First we are not yet resident, applications are awaiting documents for completion, although we have applied to join French health care having obtained our S1s. Second I have also started to apply for registration of a UK registered panel van too, that is quite straightforward give or take, but as with the MH needing residency to obtain registration, or pay a registered motor dealer/garage.
What threw me today was we called our (large) French insurance agency who have insured our French car for about 10 years, they are superb. We are getting an insurance quote for the panel van no problem, but can't be quoted for a MH over 3.5 t. When asked why and if not where do we go they didn't have an answer apart from ask a MH dealer locally.
I also realise that the Controle Technique is different for standard and heavier MHs, that the heavier ones have other aspects tested too such as the gas and electrical power systems.
As anything 3.5+ t is starting to sound more complex than a 3.5 t MH I wondered if anyone reading this forum had actually been through the whole sequence for a heavier one.
As we all know we have just 90 days to register both of these vehicles before they have to leave Schengen, the few older reports I have read re 3.5+ t MH registration have taken 6 months or more to get to completion.
We are in France permanently as of now so having our vehicles out of Schengen would be a pain, but as said that when this large very efficient insurance agency said sorry, can't insure your MH with us it started to make me think is the complexity worth it.
The MH is 2006, Hymer Mercedes in superb condition with proven only 19,000 miles from new, we are intending to ship it to the US at the end of next year but registering in France first could end up being very complicated, very loath to let it go though.
For us it's just one of the challenges that many of us face at the moment with two major crisis playing out, if this is the worst we are doing better than many.