Get an old wire coat hanger. Stretch it out as per the photo below. Keep the top bent bit so that the chook does not slide off:

Coat chicken in favourite spices, stuff if you want, tie legs together and insert wire through chook until resting on bent wire:

Take about 600mm of aluminium foil:

Fold over and join both ends. Fold ends together several times to seal ends.

Form into a circular tube that leaves plenty of room (about an inch) around the inserted chook.

Insert chook. While your helper holds the chook inside the tube by holding the wire, pull the top together to from a sealed top around the wire - like a bell:

Having started a good fire few hours ago (did I mention that earlier???) so that you have lots of coals, hang over the coals about 3" inches above the coals:

After about 5 minutes, if the height is OK above the coals, it should start to drip chicken fat into the fire, which burns and also smokes the chook. If dripping too fast, raise the chook. Dripping too slowly, lower.
After half an hour hold up by the wire to look under and see how it is cooking. It should be going brown with no burning. Adjust height to suit. It should cook the same for the weight of the chook in an oven. The heat gets trapped in the bell, evenly cooking the chook if at the correct height.
Sit back and enjoy the camp fire with a cold drink or wine as you watch and savour the aroma of you cooking chook.
Keep the wire for the next chook and throw the bell into the bin.