I am not sure if this will be helpful, but we use heavy duty L-shaped brackets in a bit of a different way than USStrongMan (clean install btw!). They are commonly available at Canadian Tire. We attach them to the tubular bars using u-bolts. A few minutes with a hacksaw, a file, and some spray paint makes the install look pretty good. The brackets in question are "Corner Brackets" by Hillman. They are about 10" long on the run, and about 1/4" inch thick so they are plenty sturdy, and this option negates the need to drill holes in the rack which can compromise your powder coating and allow moisture ingress that will rot the rack from the inside.
The brackets in question; the holes align with the nuts that fit into the extruded track on the back of the awning:
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The U-Bolts:
MotoMaster Trailer U-Bolt with round end is great for trailer axles, frames, side rails and other components | Canadian Tire
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The only thing we do is we use a bit of rubber tape between the mating surfaces of the bracket/bolt and the rack to preserve the powder coat, and we replace the u-bolt nuts with Nylock nuts of the same size. We've been using the same brackets and u-bolts for about 8 years and never had a problem.
However, like USStrongman said, I think I would exercise caution around the bars in your application. If the front-rear rack bars are not tied together, even a 30lbs awning will put rotational strain on a single bar and the mounts may not be designed for that.. If you have crossbars, then aligning the brackets with the cross bars might be ok. What I'm thinking about from my perspective is that the awning will act as a lever on a singular bar, but if that bar is tied into a bar on the other side of the car with a crossbar (making it more of a traditional cage rack), it will serve as a counter to that lever force.