Also have the 340 and this has been my experience almost to a T. I did a brisket this past weekend, 12lbs before trimming, and it took just short of 15 hours. Ran it LO for the first 6, and then up to 225, and finished at 235. All have been fantastic.
I did very similar but put my rub in with the olive oil and marinated 6-8 hours before throwing on the 340. Finished on a flat top griddle to sear. Was fantastic in street tacos.
I just picked this up from lowes, LINK , and its the perfect size for the 340, plus a few bags of pellets to store out of the elements. Thankfully I got it yesterday, right in time for snow and sleet to hit us here in KC.