Bone dry cargo carrier
Went on an 1100 mile trip during the summer of 2010. This bag is definitely hard to work with in any type of weather, even in temperatures that exceeded 90 degrees. It is because the material is so heavy duty the zippers have a hard time forcing the bag closed. But through tough southern rain storms this bag kept everything inside "BONE DRY". On the return trip I did not use the bag as I found it was too difficult to use. I also saw a 2 mile per gallon drop on average while using this cargo bag vs. the return trip. I do not know if the mileage drop is compatible to the hard shell cargo carriers.

The hardest part was the adjustments of the straps, This will take awhile but when adjusted the cargo bag was on rock solid. I even tried to push the cargo bag from left to right and it did not move. The car actually moved when I pushed it and the bag stayed firm. I used it without the optional cargo mat and have not noticed any scratches on the roof.

This was the cheapest and most reliable bag I found on Amazon considering the customer reviews I read. There were cheaper but had lousy reviews so I picked this one based on the reviews which are mostly correct. I would of given 5 stars if the bag wasn't so hard to work with.

Rain-X Cargo Bag - Good, but only the Hulk could easily zip it
The Rain-X cargo bag is made out of really tough stuff: thick and water proof. Unfortunately, I must echo the other reviews that zipping the thing is a challenge. It's doable, but it takes effort. I'm not sure my wife, a petite 5'3", would be able to. We also got a lot of cargo in it, saving us valuable real estate inside the van. It didn't rain while we had it packed, but it did rain heavily after we unloaded it but left it on the roof. Some moisture did get in the bag - perhaps 2 tablespoons. I'm positive the water entered via the zipper, which is overlapped by the material and secured by velcro. We were doing 60+ mph in heavy rain, with the bag empty assuming whatever lumpy shape. Had it been packed, it may not have leaked. The price was reasonable and I would recommend it. I just wish it was a little more flexible and easier to zip.

Worked great!
Just came back from a 300 mile trip where we used a car top carrier for the first time.
Once we got the straps adjusted for our roof rack and tightened it down we never had to touch it
until we arrived at our destination. It never made any noise or moved.
Some people have complained about the zipper, but it seemed fine to me. It is a heavy duty vinyl
that SHOULD have a heavy zipper. Don't know why we waited so long to buy one!

As Expected
This bag is what I expected. It is very weather proof. I had no problem with the zippers other than new stiffness but I was not in cold weather (some reported problems with this). The tie down straps are nice as they can unbuckle easily. I personally prefer a ratchet strap for a tighter tie-down and recommend this to others. It seems to be a good product and am pleased with my purchase.

Good, as expected
WE had the same troubles as everyone else...the zipper is a little difficult to manipulate, but it is great in all other ways. Waterproof and durable, we have a Honda CRV, and it worked great!