When we remodeled the two panels that Abe's dad had found in the junk, we used PEX pipe. It is a lot cheaper than copper and much easier to install. The setup worked well, heating water consistently to 125 degrees.
[flickr set=72157625107002735 photo=6 shift=59]
However, on two separate occasions, the PEX split. The first time, we replaced the pipe, and made some adjustments to our design. It worked fine for a long time, but then recently split again. I guess it just gets too hot in there.
So we have now bit the bullet and replaced the PEX with copper tubing. It is more costly, and you have to be very careful not to kink it when making the required curves, but we got it finished and back up in place in half a day. In fact, we got it done so fast, we didn't get a chance to take photos!
Hopefully, that will now last.