Back in the 1970s I remember a QST article about a similar antenna design for 6M using PVC pipe. The quad spreaders and center boom were the standard design but it used four "booms" of PVC to impart rigidity to the spreaders.
I'm not sure this design would work all that well structurally when scaled up to 20M dimensions. You would end up with a big, heavy antenna with high windload. Plus, in your neck of the woods, there would be all that exposed spreader area to collect ice.
Sounds like you would be better off with a standard quad.
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