The channel is 1" wide and the slots are about 1/8". I bent it by hand over a piece of padded fairly large diameter pipe. In the first picture you can see the marks I put on the channel to estimate the bend location. The haze around the bend was due to the anodized surface crazing. To keep the bend smooth, I inserted strips of thin aluminum into the slots to fill the gaps snugly. This prevented the outside aluminum from simply collapsing into the slot. It was bent to an eyeball acceptable shape. Once bent and cut to a rough slightly oversized length, I fitted it over the door and marked and cut off the internal flange and web at the ends so the outside flange would fit snugly over the Poly and door. I didn't trim to length until after the whole thing was clecoed onto the door frame.
As far as the Polycarbonate is concerned, I fitted it to the H channel first. The internal contours are more than I could have estimated. Then the poly was fitted to the door frame using clamps. After everything was good drilling and clecos replaced the clamps. The Polycarbonate was trimmed to it's final shape and the H Channel was then marked and trimmed to length, painted, reclecoed into position and finally riveted. I found some black aluminum rivets on line as black is my interior color and I wanted everything to match.