In my new S the floor cover in the back slides around. I experienced the same in another S. The problem is easily fixed. The Velcro (klitteband) fastener IS there in 3 spots on the loose cover, but is missing on the fixed bottom cover.
Just get some Velcro self glueing patches and put on bottom: left, middle and right. The cover now stays in place nicely.
Just get some Velcro self glueing patches and put on bottom: left, middle and right. The cover now stays in place nicely.