Actually, it's the other way around. Sealing will prevent air from entering, which causes Lower temps.
I often smoke at 175-200. Especially for pork shoulder - -> ideally at 205°
That's a big deck! Ours is close. I just finished refinishing it...my whole body is wrecked.
Good news - Looks like we are upgrading our grill. Rec Tec is a front runner to me, but I can't seem to find many unbiased reviews of the Trailblazer. Amazon certainly scares me, with only three...
I can attest to the fact that it makes sense not to seal in this manner...in most cases. Fire needs oxygen. The auger box just doesn't provide enough most of the time.
However, I would consider sealing it if you could not maintain smoking temps. If the temp never stayed low enough then it may...