about the air pumping and rust!
My ideas for attachment of the sheet metal collector is to bend then drill bolts through, then tighten to clamp it down against the pipe. Labor intensive, but no need to use the tack-welding methods they use at sheetmetal shops to connect. I wonder how solder would work...May try that.. could even do it after it's clamped.
I'm going to try to pick up some sheet metal tomorrow and try out a small sample piece with the kids and see what we all think of how to attach.
Flat black engine paint is a good idea.
My friend is using an air-heating system and he likes it, but he wants to upgrade to water to transfer thermal E more effectively, so I think I will not go that route.