So the problem is that Turkey tends to be dry from the git-go. There are kits out there for the cook to use a plastic syringe to inject moisture into a commercially raised turkey, to keep it moist. A fire is absolutely going to suck the moisture out of the bird, even with
barding (covering the outside with pork belly strips or bacon strips)
What about rotisserie chicken, why can't that work for turkey? Rotisserie cooking is a controlled environment of 450°F, where the humidity is maintained, and only for an hour, and chickens have more fat. A domestic turkey is leaner. (A wild turkey is so lean it would likely be a disaster over a fire.) A campfire being open, causes all moisture to leave, and the temp is difficult to fine tune. The fat a juices will drip off and burn in the fire.
I'd suggest that if using a campfire, you do two methods to complete...
PHASE 1
You build a fire in a hollowed out area lined with proper rocks, and two to three rocks the size of medium hen's eggs. You truss up the turkey on the spit, leaving access to the body cavity. When the rocks are good and hot, you drop the hen's egg sized ones inside the turkey body cavity, then cover the turkey with two (2) wet cloth bags (take pillow cases, poke a hole in the closed end for the end of the spit to protrude. Put the wet pillow cases over the bird, tie the open ends shut. Scrape out the fire from the pit, leaving only hot rocks. Have heated twice as many rocks as you need to line the bottom of the pit, Remove half the rocks, and place the bird & spit covered with the wet cloth on the remaining rocks in the pit. Put the other hot rocks on top of the cloth covered bird and spit. Cover with a piece of canvas, and then with dirt. Wait about 90 minutes. Uncover the bird.
PHASE 2
You will have a moist, cooked (steamed) turkey, without browned skin, and any flavor that you have will be from any rub you may have applied before cooking. GENTLY remove the cloth, and then put the bird on a second fire that you have made of coals and the supports for the spit. Using the spit which is already holding the bird, put the bird over the open coals. Brown the skin, and baste the turkey while doing so. Once the skin is brown you're done.
TRY THIS AT LEAST ONCE before the actual holiday.
A simpler option would be to use a smoker, and slow smoke the bird at low heat for many hours. There are lots of websites that show how
LD