Hey TTK,
Since I have a grey interior and its pretty light, I have the weather mats on all year round.
This is what I use: Weather Mats
The material is all rubber, and catches all the water, sand, salt, snow, etc.... holds up very well. With all this snow we've been getting in NY, I was able to give it a nice trial run, and its doing its thing.
The front (2) are a great fit, the anchors that lock in are dead on. The rear (2) mats you will have to match up with the floor anchors, and just notch it out. The only thing that sucks is the 2 rear mats are only for the floor, and since we have that big hump in the middle its hard to protect that piece. And with the cup holders down I found that some of the passengers who sit in the back and have beverages, it may leak out onto the armrest, then seat, and possibly the carpet. I've actually taken a piece of shrink wrap, and wrapped the hump, its not the best looking, but will serve its purpose.
I also have the cargo liner, which is a very good fit, and has a tall lip in case anything spills back there. I keep everything back there, all groceries, packages, etc... in the trunk, its what was meant for. I try not to keep anything in the car itself.
Its unfortunate that weathertech doesn't make the all weather liner, which is exact fit as well, but has a lip to catch everthing inside. Most other cars are made, but not our GS.
Check between weathertech.com and autoanything.com to compare price, it usually works out to be the same price, so I end up getting it direct from weathertech instead.
Good luck.