If you need help overthinking something. . . .I'm your man. lmao
You placing the locker in your garage? Outside?
Reason I ask is because I was thinking about your need for a vent. If you feel the location you are putting it will require a vent, AND you want it airtight, I have an idea. Get some 1 1/2" PVC such as what you would use for drain waste and vent in a plumbing situation. At the top of it you can plumb in a female adapter. They sell "Ventless adapters" for situations where you add on a sink, tub, etc., but cannot tie into the other vents in your plumbing due to whatever reason such as studs/drywall in the way. It is not always up to code in some plumbing situations, but they sell them because they have a purpose. What I don't know is if they are like a one way check valve or if they just slow down the flow of funky air.
I guess the other option is to plumb in a makeshift p-trap. This would allow the smoke to exit the locker but wouldn't completely fly out the top of the locker without soaking the clothes in a nice layer of smoke.
How ya like that for overthinking it Don? rotflmao