Rock & Roll Bed - Back Seat Use?

Does anyone know the legalities of using a rock & roll as back seats?

If they have seat belt points, do we have to buy a tested on to use as back seats whilst travelling? How do insurers feel about this?

I know someone who has a vito van and placed normal back seats in the back. He phoned his insurance company and they said because they weren't factory fitted they wouldn't insure the van?

Ideally we would love to be able to use the seats in the back whilst travelling?