Similar to the above, I built a roof rack for my Jeep XJ using another fence gate and 2 lengths of e-track. I cut them up, added some tube and welded everything together. It attaches to the OEM rack that has a capacity of 150 lbs which is fine for my needs. The e-track has plenty of latch points and accessories BUT as I thought it might, it “hummed” while driving. It was a kind of pleasant sound but I knew it would eventually drive me nuts.
The solution to the hum was to build a wind deflector. I made it out of 16g sheet metal and mounted it using 3 light bar tube mounts. I added a 4th one to the rear of the rack for an independently switched back up light and general purpose camp light.
I still have to build a separate rack for the front. It will look something like a light bar but will house a tube with an internal pull out pipe for loading kayaks like on the trailer rack above. I will only install that rack when we take the kayaks but not the trailer.