Yo Fenix...
I've grown in a crawlspace/on a dirt floor for years w/ no problems.
The area is musty due to a lack of airflow. You will have to change this *anyway* to grow weed..so the smell will go away after you turn your fan/ventilation on and bring in some fresh air. You'll also have to filter the pot smells if you are successful in your endeavor in the basement or the entire house will smell.
Ditch the duct tape idea. It will disintegrate quickly the first time it is exposed to humidity. Instad..buy sme 2 x 3 studs or find real studs and build a room....then drywall it or stretch "panda" plastic on it. Cover all surfaces.... floor/walls/ceiling.
Ditch the Co2 idea too. Your time will be better spent reading and dialing in the other parameters (temp, humidity, light, ventilation, care) that will make MORE of a difference than any potion or application of "Co2" you can give em at present. The only way I'd say "go for it" is if you are prepared to buy a regulator and tank..or a generator and a controller to make it all work properly/intro the correct amount of CO2. (down the line, bro..down the line!)
focus on lighting, ventilation, and making the space light tight....those are key.
good luck
bt dt