Please help me to make overnight cooks a success. 18"WSM. After many Minion overnights I still have problem getting the temps to stay up for more than 7-9hrs despite a full ring, 16lit Kingsford to start and dialing the vents from full to less than 1/2 at 200. Settles in at 260-270 for a 6lb butt last night than temp drifts down to low 220 and down after 7-9hrs. rained hard this am but no wind and tems in high 70's. What tricks have you learned to have a ring last 12-16hrs. thanks