Nice! How are you sealing in the copper tubes? Are you going to pressure and leak test??
Since I got the tubes from the Hobby Lobby behind my neighborhood they're actually brass, but if I invested a little more I could have ordered some copper off of Amazon. I'm not worried about corrosion, seeing as brass is a copper alloy.
That said, they are going to be sealed with epoxy, and I hope to create some aluminum fins that will be stuck on with thermal adhesive after I cut them out of the sheet with tin-snips and drill the holes. I already have a template made up for that.
I'd like to do some actual testing with it yes I just did a simple leak test with my water faucet, didn't seem like much leakage occurred with a simple pressure seal.