Excellent product. So much more convenient than tarpaulin+ropes+bungee cords. We did a 2000+ km drive on a Honda-BRV and it mostly didn't let us down.
Driving through light to moderate rain, contents were well protected and there was no dampness inside the bag. But during a particularly heavy spell, some water entered the bag, probably through the zippers, my inexperience also might be to blame. Thereafter, I was very careful to ensure that the flaps covering the zippers were properly folded down and velcroed.
Note: This bag must be placed on top of a roof carrier only (and not directly on the roof). Sheet metal of most car roofs will buckle under load.