Roof bags for a car - do you need roof bars to use one?

[DeleteIfNotAloud]

My car has built in raised rails to attach roof bars to, but I don't actually have any roof bars. I was looking at buying some but then I spotted roof bags like these which seem to say you can attach them to just the rails without needing roof bars as well?

Is this true, wise MNers, and if so are they any good?

I have an Amazon version of one of those (couldn’t tell you which one). It’s 4 years old, lives in a shed outside and has been brilliant! Takes our big suitcases and a lot more when traveling. Keeps them dry. It feels secure when driving. Mine attaches to rails on the roof. It’s easy to fit (but takes a bit of practice). DH and I can now get it up, secured, and loaded in about ten mins.

However the disadvantages - it’s not as safe as a roof box (I bought a tiny padlock for when we stop on long journeys but it basically zips closed, and/or could be removed from the roof by undoing the clips) so we put it up and load it the day we travel (which for our frequent 3am starts to get to the ferry, is slightly painful).

Thanks, this is promising! We live somewhere safe and secluded enough that putting it on and loading it the night before will be fine.

Some require bars or rails, some strap through and across the inside of the car - check carefully you have ordered the right one for your set up... (and don't let your H order it if he has form for a lack of attention to detail)
I tasked DH with getting one a few years ago. Our camping gear had expanded to fill the car and combined with the DCs' legs growing (reducing storage in the footwells) and an extended camping trip requiring more clothes and non-camping equipment than usual, we needed the extra space. I reiterated many times we needed the 'strap through' version. It arrived, and I asked him to check it over and have a practice or two fitting it as, like the PP, it would need to be fitted the morning we left... I didn't want to be spending hours scratching our heads trying to figure it out for the first time on the day. He said it had been done, so you can imagine the frustration on the morning of the holiday when we discovered it was one that needed rails... (He hadn't checked and practiced it. He thought I was being overly cautious so didn't bother and lied). Poor DCs spent the 9hr drive with a number of pillows and some of their toys balanced on their laps, and we had to leave the saucepans at home and buy some when we arrived. DH was only able to take what items of clothing he could stuff loose into the gaps after we had got everything else that should have been in the roof bag stored (bedding and clothes mostly). Can you tell it still makes me angry when I think of it 3 years later?

From memory, they can have issues with water ingress in heavier rain, so make sure everything is bagged within. There is also an issue with water soaking along the straps and dripping into the car with the version that strap through. Otherwise reviews were positive IIRC.