I smoked fowl for many years and always added cranberry juice to the water pan and swore by it religiously! Cause that's how my Pop did it.
Then I took it seriously and did a real blind taste and you know what, it added nothing. I totally agree with Demosthenes9.
I suggest if you want to add a flavor modifier to brisket you inject with a little beef broth solution.
I would recommend though that since you said a MES30, that you do not mop, spritz, baste, or sauce. The electric smoker really needs not to recover any lost moisture as long as you keep it closed. Every time you open the door and do anything, the smoking chamber looses heat which has to be recovered. An Electric takes much longer to recover than a firebreather, I have read as much as 15 mins. I sort of doubt that but lets just assume it takes 10 mins., If you do a 12 hour smoke opening the door a minimum of once an hour, you've basically added 120 mins (2 hours) to your cooking time, that at only 1 opening per hour.
Also look at the interior of your smoker and know your limitations. A 10+ pound packer has to be special trimmed to fit inside it. Just something to think about.
Remember electrics maintain and hold temp better than your average firebreather, but when heat is lost and must be recouped its a much slower process. The electric will hold moisture better requiring little or no additional moisture, so it offsets the slow heat recovery vs. the firebreather. Basically, just keep the door shut and forget the meat till its ready.
Now for the disclaimer...... These are my personal observations with my MES30, your results may vary, you may do things a different way, its the nice thing about smoking you never know which process you'll like best. You have to smoke a load a meat to see for yourself.