You have found the ongoing problem with thin-walled offsets. The same scenario why we insulate our household thru the attic... loss of thermal energy.
Check and seal leaks... and insulate via natural fiber (non-synthetic) blankets by draping over the smoking chamber.
Thicker steel (mass) helps with heat retention, too.
Bacon should be capitalized as a pronoun for pork!
A BBQ Servant; cooking for the Troops, Churches, and Charity
Operation BBQ Relief founding member
Lang 84 Deluxe Kitchen known as "The Glamazon"
Custom Klose Backyard Chef... of Snot, 22.5 WSM
Lang 60 Mobile - The Damsel II, Lang 48 Patio - The Damsel, and Bubba Keg Grill - RIP