If you get a carbon filter with a fan that is rated for it there will be zero smell. I was venting outside but now that its cold as shit I just vent inside the room. As long as everything is connected right it will be fine. A pc fan will not cut it for the filter. If stealth is important to you then you cannot skimp on this part.

Try looking for a 4" inline duct fan (not a duct booster) and a matching carbon scrubber like a Phresh filter. Also check out a speed controller for the fan since your grow space is very small. There are some DIY threads on here for filters as well. Ive made my own before and it worked fine but the ease of just buying a new one was too tempting. Now I use Phresh filters and they work great.