Zuber, you seem to know your steel. How about milling a slot in square tubing to make the channel? This was my plan as square tubing is easy to come by in my area, and cheap compared to other options that have to be ordered and shipped.
Blue- 2 x 2 tubing with milled slot (not full length)
Red - 1.75 x 1.75 without spacers, or 1.5 x 1.5 with HDPE spacers (yellow)
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