I purchased the 12 found it was a good tarp, well made, tried it out in a torrential down pour, and it has possibilities to be a pretty good winter tarp. However it did have a small leak. Kelty replaced it because they wanted to test the 12 and see what the problem was. The leak was small seepage along a seam.
I traded it for a 9 and have had it out in a few pretty good rains, snugged down it worked fine, with it's 13'+ ridgeline it should keep you dry in most rains.
Car camping either should be fine, backpacking, I want lighter and less volume.