Hi Richard, good info, thanks.Mine wasn’t screwed down. But it has a lot of stuff on it, so it’s not really a problem. A small amount of silicone will stop it rattling when empty if that’s what your worried about.
The ply lining kit that my van came with was awful. I lost a good 4” (or more in some areas!) space in the back each side, and it’s didn’t fit around any of the door fittings well. It as a very poor effort, but maybe that was a really cheap kit. It needed a lot of modification to get the space back.
The black plastic trims just inside the roller door can come off to get rid of that awkward lump (why Nissan! There isn’t no seat belt!) . I cut mine down to protect a cable lower down.