While I'm mainly a UDS guy, I do have an offset as well and it's a leaky bastard at that-prolly why I hardly ever use it!
While I don't have a lot of offset experience, a few things I can say is to seal up those doors and any seams as good as you can to help you hold an even temp. I also put some firebrick in mine to act as heat sinks to stabilize temps at it helped immensely. Might wanna run a water pan in there too to help keep moist and hold temp. I'm sure others will chime in with more insights. Good luck!
UDS, Akorn, Weber Red Head Kettle, Drum Grill, Gasser w/cobwebs all over it. I'm JD.