Hi Rachel,
We use the Official Eriba bunk over the single bed in a 530.
The only attachment points are a rail which fits into the table rail attachment, and two hooks which go over the lip of the roof.
There are no side attachment points, but I know Eriba only advertise the bunk as fitting a few models, so I'm guessing it may be an issue with dimensions.
If you're close (Berkshire) we'd be happy to let you try the official bunk in your van.
FB