Minion method is best for that kind of smoker.
Raise the coals higher off the bottom, so there is more room for ash to collect and not smother the fire
Try kicking the bottom when it starts to temp dive to knock loose ashes down away from coals.
Use a high quality charcoal briq such as Stubbs, (avoid Kingsford blue and other el cheapo briqs) or use a decent lump charcoal packed in tightly for better burning.
Drill a bunch of holes in the charcoal pan on the sides for better airflow to the coals.
Make sure you have a way to choke down the air intake for lower and slower cooks. Personally I'd be jazzed having it cruise @300, more sleep time.
Modded Brinkmann Gourmet. Basic UDS. Rescued 22.5" OTS. SJS Mini-WSM. Stubbs. B&B Oak Lump.
Cannondale 2009 F8 (for burning off all the great BBQ)