Rubs can pretty much be whatever you feel like adding. Most people go with the KISS concept. Keep it simple..... Salt, Pepper are the basics, then you can add in whatever you like, Garlic salt, seasoned salt, cajun seasoning, creole seasoning, etc. Let us know what you do decide to use.
Beer can is one of the best ways you can cook the whole chickens, certainly will help keep it moist and flavorful. The hardest part is that you can only drink half that can of beer. (Of course, Force still drinks the other half after cooking, but we don't recommend that.
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Take some pictures and post them up, we would love to see how it comes out..