HEX 2

Are those fins on the side and the whole PVC pipe rotates for improved circulation?

You got it. The photo's a bit dark, so I'll take a better one, but the inner pipe has an end cap glued on the bottom so it's watertight, and a bolt through that end cap goes through a hole in the flattened copper pipe and has a nyloc nut to hold it in place and prevent the hollow tube popping up when the HEX is filled with water to cover the coil.

The four vanes screwed onto the inner pipe give it just enough clearance to rotate freely without touching the coil - kind of like the mangler in an old-fashioned washing machine, but only going one way! It certainly keeps the water moving and circulating around the coil, preventing any heat stratification/hot spots or whatever.

Photo - see HEX_4