Adapting roof rack accessories / mounting things to squares

I will admit, this may be a nitpicky problem, but I have an old set of Thule kayak attachments that I used on my 4Runner. They, like I assume most Thule/Yakima/generic attachments are designed for aero bars. How are people mounting these to their rectangular crossbars? As you can see from the pictures, they... sorta work. I'm not worried about them coming off but they're only held on by the corners of the brackets and as tight as I want to make them, they still slide and shift when there's weight on them and are probably doing some light damage.
I'm sure I can swap the bottom piece for a flat tab of metal with maybe a strip of rubber or something between, but the top is still barely holding on. I haven't had much luck finding a solution either via hacks or an off-the shelf option.

I know I can't be the only one to run into this, despite what the lack of results of my searches might say. Any tricks or more polished adapter-type recommendations people are using?

 

What is it that you’re trying to
Mount to the bars?

 

You could use two pieces of flat stock metal with 2 holes drilled- one on the bottom to replace the current one, and then another between the kayak rack piece and the cross bar. You might need longer bolts but should take care of the fit issue

 

You know, I can't explain it but for some reason the second piece of metal just... did not occur to me. I'm sure that will work fine, although I think I will need a bit of rubber to give it some grip.

 

Sometimes it just takes another set of eyes on a project. Plus I just went the opposite way of fitting kayak mounts on round bars

 

I have a set off Thule HullaPortII kayak mounts that I put on my Yakima rack, i had to go to longer bolts, so I decided to go with stainless bolts with a. real aircraft style locking nut and washers, and cranked them down. I now also have a uptop overland cab rack, so i could mount 1 kayak flat across without the thule rack, so I only use the Thule when I need to go with two kayaks

 

Very true. Good looking setup! How did you adapt them to the round bars, out of curiosity?

I think I'll end up with a couple of sets of those vertical mounts eventually. I'll probably go with the ones that fold down so I can get in the garage without removing them every time I want to use them. For now, I already had these, and I can throw an extra couple in the bed when necessary.

 

The Yakima Jaylow kayak mounts fit the prinsu style crossbars perfectly. That’s what I use with my RCI rack.

 

It looks like those use the kind of claw style clamp like the cargo boxes. I'll keep that in my back pocket for when I upgrade. Thanks

 

I use Malone gunwhale kit on the square bars for our canoe. Fit looks just like yours but once everything is tightened down there is zero movement.

 

Yes sir. They are a tight but very good fit on the 80/20 cross bars. I don’t have a picture of them handy sadly.