Is it true that the 100.39in width rule has now gone?
Dont bank on it, depends on which office you choose to register, as they dont know the answer themselves
Can you get multiple seat belts fitted to accomodate the kids or what are the rules on them?
Most Rv are fully belted
can you simply hop on the ferry and travel Europe or do you need something else done apart from green card insurance?
Yes but Green card not reqd for most of Europe but for some fringe member states eg Moroco it is (check)
SVA Not reqd for Motorhomes, straight forward registration is all.
Geo