I usually use my hydropack which has a nice feature of being able to seperate from the drinking tube so you don't have to fish it through the hole to take off the bladder and clean it. Also has a really nice large opening and reverses. I hate the valve though so ended up using the connector to go into a camelback hose and bite valve.
http://www.jensonusa.com/store/product/HY299E00-Hydrapak+Reversible+Reservoir+Ii
.aspx?sc=FRGL To keep it cool I have some reflectix insulation that folks use in attics it is basically two aluminum foil layers with bubblewrap in between. I made a pocket for my water bladders and found it actually kept them too cool on randos on 100+ degree days until I learned to put in just enough ice rather then filling completely with ice and then adding water. I could actually fit the whole affair over the bladder in the fastbacks as long as I didn't fill my bladder all the way up either with camelbacks or the hydropacks.
In the hurricane for my commute it would keep the water nice and cold sitting in the parking garage all day and be ready to cool me off on the way home. Potable ice or water aren't something provided at work so I had to go that route.
Also I know some folks blow back the water so it doesn't sit in the tube but I was pretty sucessful using some mylar or aluminum sheathing on the tube to keep it cool. The black stuff that keeps it from freezing in the winter works ok but it is so much better with a reflective sleave.
Re brainbox/fastback. I used a double century fastback which I think is basically a 70l on each side along with a brainbag, aeropod or aerotrunk and they worked well together. I actually would have both bladders setup on longer rides one with plain water one with something in it but I do drink alot I don't think I ever noticed anyone carrying half the water I did.