Jessica, I have one very similar to the one you've pictured and have had no problems with using it, whatsoever (and I cram a lot of plant in it in summer!). I have had it for 2 years on a 2nd floor balcony and it has survived everything from 100 degree days to pouring rainstorms, to 30+ mph winds (secured to the railings with bungee cords). I can't speak for winter, as I live in Wisconsin and I use it indoors without the plastic cover to keep my plants under my grow lights. Because of the open bottom and the big door, I don't think the off-gassing will be a problem. During rainstorms, I usually zip down one side of the door and only partially zip the other side, so that there is still some air flow. Nancy

That's a lot of work, Amy. Why add a vent at all? Could you not just unzip the door and vent out through it? Or, are you trying to put a vent somewhere across from the door so that there is air flow through the greenhouse? In a greenhouse that small, keeping plants from baking insie it might be a real chore. Generally, the smaller a greenhouse, the harder it is to get good venting and air flow because heat builds up so rapidly in a smaller greenhouse. The greenhouse effect is real. Even with a larger greenhouse, I keep the doors (and sometimes all 4 vents) open most days, opening them up as soon as the air temperature rises to 33 degrees, assuming it even had dropped below freezing. If we don't drop below freezing, I open the greenhouse as soon as I walk outside early in the morning to let the poultry out. I have 50% shade cloth on the greenhouse year-round. It still can hit 145 degrees in there just an hour or so after sunrise on a winter's day. Running a fan can help promote air flow and push the hot air out of the greenhouse, but I try to restrict running a fan only to the hot weather months, not the cold weather months. Clearly the solution is a bigger greenhouse. (grin) But, you knew I'd say that, right?

If you have somewhere at the door end to attach a clip-on 15cm fan and cut a 30cm 3-sided flap at the other end it would be functional all year long.

You can use it, but it is not UV protected and will probably not last you a full season. It will get yellow and brittle. You need to use 6 mil, 4 year greenhouse film. It is UV protected. The 4 years refers to how long the UV protection is warranted for.