Bad news - I just took a look at a few 2012 5 seat berlingos - VTRs and XTRs. I lifted the carpets - they were all the same - a plain corrugated panel without fixings for an additional row of back seats. My theory - the 7 seater is a factory option where they weld in an additional floor panel, complete with fixings. If that's true, I'm not going to be able to safely retrofit an extra 2 seats without a "bodge" that would be difficult to insure, or if I didn't declare it would invalidate my insurance. So it's a no go :(