I agree with Randar that if you are having moisture problems you may want to use a slightly higher temperature. Lots of people advocate temperatures that are too low which lead to the cook taking excessively long which leads to moisture loss. This was exactly the problem I had with my first brisket cook.
You said you cooked it at 225 degrees, but was that the dome temperature (the built in thermometer) or the grid temperature (from some other thermometer sitting on the grid)? That is definitely too low of a dome temperature.
I would suggest starting with a full, uncut (packer trimmed) brisket if you can get it. It will have the point and the flat together with lots of fat still on it, and it will be upwards of 12 pounds. It is more likely to be moist in the end if you start with one of those rather than with only a flat. A pre-trimmed flat is about the worst to start with in terms of moisture. If you can only get a flat then I would brine it overnight first (I don't brine packers but I would brine a flat) to get moister results. Foil can help retain moisture, but it leads to mushy bark which I don't think is a good tradeoff. The only times I have used foil is after grilling it to completion and trying to hold it warm for a party (wrapped in heavy duty foil with no additional liquids, wrapped in a towel, thrown in an empty cooler).
My own notes from my last brisket cook on my BGE:
240 degrees grid (dome will be ~25 degrees higher usually)
185 degrees target meat temperature
approximately 1-1.25 hours per pound