Review on 20 Cubic Feet Waterproof FieryRed Car Roof Bag Cargo Carrier - Anti-Slip Mat, Travel Storage Luggage Bag Soft-Shell For All Vehicles With Or Without Rack by Steven Doty

I can confirm that you can use this on a car without a roof rack. The straps go through the doors and connect inside. You do have to figure out what to do with the excess part of the straps. The container will tend to slide toward the back of your roof so I recommend angling the forward straps forward at a 45 degree angle into the doors rather than 90°. The pad that goes on the roof and under the container can flap in the wind so I recommend rolling up the excess and cinching it down with zip ties. You will also find that the wind can cause the pad to bunch up and slide underneath the carrier to some degree, as shown a picture from another review. It ended up being a wedge that kept the front end elevated. The carrier did not actually touch or mar the top of the car. I also suggest finding four small pieces of cloth to go between the straps and the surface of your car where they enter the doors as additional protection from scratching. I did this and the paint looked fine at the end of the trip . I put one large suitcase and two carry-on sized suitcases in the carrier. There is room for more than that. I suggest stuffing clothing, towels, or pillows around any wheels on suitcases so they don't contact or damage the material of the carrier. It worked well on the 250 Mi trip we went on but it does show some very minor wear and tear. The price is right given we plan on using it infrequently. If you need one to travel a lot or plan on going thousands of miles you may be more satisfied spending 2-3x more on a hard shell carrier.