My concern is will there be any health issues with copper in contact with the meat?
Ron is incorrect about some copper cooking pots. There are many that are solid copper. There are also copper tea kettles not to mention the pipes that carry the potable water (both hot and cold) in many houses. Modern copper piping is lead free so I would not expect any food contamination problems. There is really no reason to not use a steel pipe or a stainless pipe.
Kev79 first, the copper in a copper bottomed pan is not in contact with the food but underneath the steel or aluminium the pan is made from. It would not be dangerous health wise to use a copper tube, but there would certainly be a chemical reaction between the copper and the naturally occurring acids in the meat which would give rise to a nasty taste, if your talking about a whole lamb and there is no alternative, wrap aluminium foil tightly around the copper tube.
Research how they did it in medieval times, I am sure it was never copper, I am sure it would taint the meat anyway. If your doing a proper BBQ then cut it into slices, chops and shanks anyway, it will be much nicer and not so dry. It all sounds great having half an animal on the spit roasting away, but it is dry as ### and people will talk about that crap BBQ for years to come. There is another way to have succulent lamb, which is to bury it to cook it on red hot rocks. You will also find that recipe on the net which is gorgeous, moist and never dry. The longer you cook lamb for the dryer it gets......What a waste of such lovely meat!!
The heat, weight and rotational flex will bend the pipe and screw everything up. That's what you need to know. But since you're the creative type, go to the hardware store and look at a grill that has a rotisserie. Check out the design that keeps the meat turning over the fire and not the bar turning in circles while the meat just hangs there. Then scale the whole design up and fabricate it yourself. Steel/iron bar. Stay away from galvanized.
Copper pipe is an alloy - not pure copper. I would not recommend it. Copper is also too soft - it may bend in the heat of the barbecue, especially if weighted down with a heavy piece of meat.
