If I understand the question correctly...I think your temp on the smoker are fine. I usually try and do 250 but 220 is fine.
As far as getting to 170, yes when I get there I foil it. With that said, you can do one of two things. The purists will keep the brisket on the smoker until it hits the desired internal temp. At that point, you won't be getting any more smoke in the meat as the pours have closed.
Since I live in a colder climate, I simply take the foiled meat and put it in the oven at 225/230. I like the lower oven temp as once it's in the foil, the temp will climb pretty quickly regardless of being on the smoker or the oven.
There are a lot of ways to skin this cat and alot of good advice out there. Frankly, the next one I try I am going to try searing it first per Smokyokie's recipe.
Here are a couple of briskets I posted:http://www.smokingmeatforums.com/for...ad.php?t=14461http://www.smokingmeatforums.com/for...ad.php?t=14079
I'm not an expert by any stretch on these but I like to try new things and see what happens. Hope that helps.
Let us know how it goes.