I've looked at a LOT of user installation reports, but I do NOT recall ANYONE using Angle Extrusion rather than Circular Rods. Obviously, Angle Extrusions would have a MUCH higher wind resistance....and may or may NOT break sooner than Rods....it would depend a LOT on the inherent strength of the chosen metal formula....I would ALSO be worried about how it holds up to wind induced vibration.
Since an outdoor antenna needs to survive high winds [esp. in your location], I would highly recommend that you stick with what we know WORKS...namely 3/8-in Aluminum Rods.
I don't know anything about metal alloys, so I don't know what the differences between one or the other signify. I mentioned that I'm not setup to solder aluminum. I'm wondering how you guys go about mechanically joining pieces together to get the lengths you need? The local hardware store or Home Depot or Lowe's is what I have available for local purchase. The longest pieces they seem to stock are 4 ft. I've found some online suppliers that go up to 12 ft, but the shipping costs completely negate any savings.
The online supplier indicates their 3/8 aluminum has poor characteristics when it comes to bending and forming.
I found this at Home Depot
The local store (45 miles away) shows it being in stock, but if not, I think shipping is free to the store.
With this square tube. I thought I could notch the end of one and slip it over the end of the other, then rivet it. It would probably be stronger than the "L" shape. I could still reinforce it with epoxy, but again don't know what effects epoxy would have.
The other consideration would then be the width. I guess spacing of the elements would be affected but I could center it on the specified dimension.
We've already established things will work even if it isn't the best choice (bed springs, toilet paper tubes, razor blades, etc.).