Well I doubt I'll be the only one to say this but you are in need of a UDS.
The offset you got, or anything that looks like it, will never give you the ability to hold temps. Not without a lot of modifications and sealing and even maybe then.
Yeah its overloaded, the quality cabinets you see on here can handle that, the COS cannot.
My UDS will suffice but when I pull thee trigger on something it wont be cheap. It'll be good but quality is not cheap.
Pete-my first UDS,a brick pizza WFO, a leaky Chargriller offest, wifes Weber Genesis gasser, and now a Lightening Fast RED Thermapen