Since you're doing flats, which I think cook best with a moderate temperature, I would cook around 250F to 275F, start with the meat on the cold side. You will want to foil, I suggest foiling at 165F internal until temperatures start climbing. Remove and cook to probe tender. A little bit of beef stock in the foil will help.
If you have time on your side, the injection will aid in moisture enough, you could skip foiling and still have a great product.
"perhaps...but then again...maybe not..."
careful there son, those ribs are boiling hot...
(='.'=) Here there be bunnies...
Pacific Rim BBQ
Bob's Brew and Que