Milan, I'm a fat cap down guy...helps shield the bare side from the heat below. Now, what probably dried it out was how you did your hold, not the length of time. If you are not going to be there to remove the meat, and cool-down the smoker, before holding at 140, you can't let it get to target temp. These smokers are tight, and well-insulated, so it takes a long time for a closed-door unit to cool from 225 to 140! I mean a LONG time. You continued cooking well past your target.
My thoughts on holds: It's best to be there when the meat finishes, for best results. Remove the meat, double-wrap in HD foil, while the door remains open to cool down. Once it's below 140, put the meat back in and set it. It can sit in there, wrapped, darn near indefinitely.
If you can't be home when the meat finishes: Program your target temp at least 10° below your target temp, then the hold. Since it won't be wrapped, it will continue cooking. Even if your brisket only rises another 5°, to 190, it will be great after a long hold.
Holding, in the smoker, is a great tool, but you have to be in control of it to get the best results.
