Greetings Dave,
When we bought our Swift last year we were already aware that although the van had breather boards in the front behind the cushions, it did not have a board behind the island bed at the back.
I had some Upvc soffit left over from building the house as well as some 'H' section jointing for the same job. The soffit was about 8" deep and it was an easy job to cut it to length and attach the 'H' section to the back and glue it in place with double sided tape. The first attempt fell off but then I found some industrial strength 'sticky' that has done the trick and kept the bed and bedding away from the outer wall.