I gotta agree with Jim......I no longer fool with marinades. There have been numerous studies that show a marinade will only penetrate to 5 mm. Now, that is OK for thinner cuts of meats but for a brisket, not much help.
I have found the secret to doing flats..that's all I cook anymore....is to trim enough of the fat cap off so that when done cooking, there is none left. This will allow the rubs to be carried down into the meat. Believe me..that takes practice...many a brisket has been sacrificed to the chili and baked beans Gods.
If you don't trim enough, the rubs stay on top of the fat cap and when you cut that fat away before serving..off comes the flavor!
They will cook up at 1 hour per pound. I learned that the hard way. Also, you need to rest those things for a couple of hours...double wrap in foil, wrap in towel and then place in empty cooler. Not to worry...mine was still too hot to touch after 2 hours!
At least that is my method....it got me a 3rd place last weekend in brisket.
Stogie