I had the same issues with my wagon & dog, at first I would just put rugs down to protect the floor, but I would still get hair on the carpet on the wheel arches, so I found this at Subaru but brought it on eBay.
Pros:
It fits 95% well, when i push it into place properly
covers all the carpet
Covers the rear of the seats
Covers most of the plastics
Con:
You need to stick little Velcro patches on the plastic to hold the top of the cover in place
Not quite a perfect fit but close, on the Subaru website it appears they have updated it & added a bumper protector & appears to be black??
You can see in this pic how the top of mine isn't attached, because I'm not keen on sticking the Velcro patches on the plastic
. I'm thinking of having a look at 3M products to see if they have something suitable, as there sticky stuff comes off with out leaving marks.