Thanks for the follow-up! I was wondering how this experiment was going.
No problem... I used less than 10 lbs of ice over ~40 hours... there were quite a few pounds that are melting in the sink now. Draining and topping off was just as easy as hypothesized. I could easily brine a couple briskets at one time. I'm pretty sure I could do two turkeys at once, as well. On top of it all, cleanup is just drying it out and when I'm not using it for brining I have a perfectly functional drink cooler. There is no question this is my go-to brining solution from now on. In the past the brining step was sometimes a stopper for me because of the effort it would require. That's no longer an issue at all.
The brisket is rubbed and resting in the fridge right now and will go in the smoker in about 90 minutes... dinner tomorrow is going to be yummy.