Billy, if injection works for you, do it! I did, was great; that time did 3--yeah--3? on Cajun stands, I think, small footprint on stand--in 22.5 kettle. Injected with a similar adding Tony Chacere's (sp) and they were wonderful!
THEN, I made life hard on myself in prep work but DANG they were killer:
On 18.5 WSM did 6 of 'em. So I had about 1 gallon + 1/2 of brine, with some pineapple juice. Brined a few hours. Rinsed well, separated skin from, a tad, and put them Cornell Marinade overnight. No water in pan--just foiled, Kblue, 2 fired chimneys on top on some unlit with a little apple wood and grape vine, dried--got WSM roaring but had chickens on as it was reaching 375 and cut back all vents to hold at 350.
Before that, popped birds on small footprint stand--wiped just a little of Cornell off, NOT all. Then some my pork rub + lemon pepper--sage, etc.--but used only pineapple juice in can with some pork rub. Stuffed upper cavity with fresh rosemary--I keep it, grow tons of it, freeze it for winter--and an orange chunk covering top "hole" of each chicken. Think I had "seal" one with lemon, but not any difference.
Recipe I use, modified Cornell, 3X for 6 whole chickens:
2 cups ACV
1 cup veg oil
1 egg
2 tablespoon iodized or 3 DK kosher (yep,after brine)
1/2 teaspoon ground black pepper
1 tablespoon poultry seasoning--see above
1 teaspoon Tabasco chipotle--or ground cayenne--any ground hot pepper will do. (I grow/dry/grind my own; El Cheapo Brinkmann does have a purpose for drying peppers, but generally finish in food dehydrator.)
I didn't think WSM 18.5 would go that high but it DID. That many took about 2.5 hours. But holding temps steady at 350: BEST chicken I've ever eaten--aside from Mama's fried--now, that woman can fry some chicken!
Good to do a bunch because I like to freeze some cooked meat for stuff like Brunswick Stew, tacos, etc.
I am so sold on that Cornell for just marinating, after brine. Most use it as a baste but I absolutely love it as a marinade. But I do NOT wipe all of it off, as some suggest. Tried both, like it with it on. Did a lime/ butter glaze on chicken quarters last week, but rubbed most of Cornell off, and I thought it was just too dry. Sounds good. My opinion is: IF YOU LIKE IT, KEEP USING IT!