Hi Rob!
I use foil every time I cook ribs. I cook baby's and keep my grate level at a steady 225? for the entire time. The ribs weigh 2 1/4lbs. per slab.
I will cook for 3 hours, unwrapped, followed by 2 1/2 hours in foil and then the last 30-40 minutes I unwrap, sauce and back in the smoker to crisp them up.
Now, there are many variables to these foil techniques. The ONLY way to find your ideal is to experiment. Once you have it nailed, then you MUST consider your temps as the most important aspect of the cook. In other words...if your ideal cook was at 240?, then every time you do ribs again, it better be 240?...or they will not come out perfect. That is because the foiling will "amplify" your temps...so pay attention to them.
As most around here know, I tend to be anal about my cooking temps. That is mainly due to my competition cooking, as the meats have to be turned in at very specific times. There is NO room for error.
One last tip....before foiling, I sprinkle either more rub OR some brown sugar and then wet it with liquid....I use some type of fruit juice with oil in it.
Good luck, Have fun and enjoy yourself!