Personally, I'd rather see something stronger than copper. I'm not a pro. I've heard that propane can cause a buildup in copper pipe as well, and eventually plug it through a chemical reaction with the copper. Again, I've not had any experience with this. You may want to call the building inspector and ask what is allowed. While you may not need a permit (depends on where you live), finding out the correct way to do it (not the easiest) should prevail. What does the manual say for the device you are installing? Probably that it must be done to local codes and may not be very enlightening, except to a pro.