We vacuum seal our non selling roos. Before sucking out the air and sealing the bag. Try adding a brine or broth in the sack. Rosemary twigs, sage leaves and or any of your favorite herbs. Slowly thaw in your refrigerator a day or two before your bbq... Not in the sink. The herbs slowly intoxicate the flesh during the gradually thawing process. Then rub olive oil for a crispy epidermis. Beer can chickens can also continuously hydrate the meat to help avoid rubber dryness. Doesn't have to be beer in the can.. Drink the beer and fill the can with h2o/herbs and spices. Garlic and onions rock!i butchered 2 roosters about 12 weeks old a month ago put them in the oven 3 hours after getting done, toughest bird I've ever eaten. Had me scared to death about the 50 red broilers were doing this weekend, but did the last rooster last tuesday and forced myself to let it rest in the fridge for about 38 hours. Absolutely delicious.....
I really didn't think the whole resting thing could actually make that big of a difference but I will never not rest fresh butchered birds ever again.
I've also heard if you rest after thawing it will be better. I'd wait two days after thawing and give it a shot if that doesn't work then onto low and slow.
Good luck!