Agree with Ron. 6 hours at 250 with 2 of those in foil should completely destroy a rack of spares. Double check your cooking temps and be sure you check the grate temp. Maybe consider cooking with out foil or revise the 321 methods to a 2-1-1 or 2-.5-1.
18.5" OTS, 22.5" OTG, CB Silver(Rip), Vintage Coleman Bullet, Pit Barrel, UDS