The "liner" bit comes in that it's got the lip all the way round to stop stuff dropping down to the lower level, the grott that you may be shifting on the tip run or muddy boots etc in the back. A standard carpet mat like the anti slip one I've got from the Seat catalogue looks good, does the anti slip well, doesn't block off the storage areas but will allow grott to fall into the low level boot. That is how I see it. (including holes in my boots bag where I still get an issue... change the bag

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So the liner is more practical for dealing with dirt but effects the side storage if it extends into them. I'd get one of those if I started another house clearance and swap back after keeping it in the garage - lucky no more house clearances, tip runs, charity
shop runs and moves in the near future. Expect the liner is good for dogs as well. Horses for courses.