I didn't have any leakage problems, since the gaskets under the roof rack are not designed to stop water. I just cut a small piece out, andfit the bracket in.
The bracket is from a CB shop here in town, I have no idea who makes it, but they make dozens. Check a truck stop on an Interstate near you, and you will find a large selection of CB goodies.
I moved it to the ARB because it was too noisy on the roof. Any branch that it contacted made it wiggle back and forth, and it echoed throughout the cabin.
I also had an EZ-Over on it, so I could lay it down flat to get in my garage. If I wanted to use it on the highway (for traffic reports, etc.) I would have to stop and stand it up.
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