Cyber,
They look fantastic!!!
The only question I would have is how does the PVC tubing cope with the heat? I'd be a little worried about fumes being produced from the PVC as it heated up. It is a very small are inside the tube, and it would be a lot hotter inside it than it would outside.
Apart from that, it seems like a very good idea. Although have you thought about using metal piping? Then that way the heat tape through them could be operated on a thermostat.
