I have one of these that I use in a BMW wagon (started poking this forum considering a replacement for that car):
Looks like that one is out of stock, but a number of mostly identical ones are available.
Our Briard, a bit smaller than a Newfie, but almost as much fur, spends about 8 hours a week back there, so it's seen lots of use. My SO repaired one of the straps after a chewing incident and now the side connection is looking a little torn. On the one hand I might try to find a higher quality one, on the other hand it's probably fine to replace it once a year, at those prices it's basically disposable.
I really like the fact that it forms a tub so anything dragged in by the dog remains in there and can be vacuumed out without going into all the seat crevices with a tool. I would not skip that feature.