Get your camp fire to a point where there are plenty of hot coals in the pit.
Place two chickens in large stock pot. Add salt and sugar then fill pot with water to cover chickens. Let chicken sit in brine for at least 4 hours or overnight. (Refrigerate if letting sit overnight).
Truss your chickens (Watch this video if you've never done this before) and skewer the chickens firmly onto the rotisserie spit over your campfire.
Combine apple cider vinegar, brown sugar, white pepper and water or beer in a squirt bottle. Douse chicken with this mixture.
Rotate spit every 20-30 mins (10-15 if your fire is roaring). Add wood to the fire as needed to keep fire nice and hot but don't let flames touch the meat. Douse chickens once an hour with brown sugar and vinegar mixture.
Cook chickens for 4-8 hours depending on how hot your fire is. Chicken is done when thickest part of bird is 165˚. Let meat rest for 1020 minutes before carving. Top with barbecue sauce and serve.