It would definitely help to have a fan. I bought myself a good quality thermostat (about $50) and it turns on the fan when it gets above my chosen temperature and turns it off when it drops back down. For a fan, I just got an inexpensive room fan at Home Depot (about $30) -- with a plastic housing so it's rust resistant -- and clipped it to one of the greenhouse shelves. It's all I need to keep the air moving and to cool things down. With that addition, you should be able to grow a variety of vegetables, as well as some more fragile things, like palms or tropical (clumping) bamboos, that will winter over successfully if you add some supplemental heat in winter to keep things above freezing. I have a number of exotic flowering plants from places like S. Africa that bloom in my greenhouse and are safe in winter since I keep it at about 37-38 degrees F with an electric heater.

In torrid Alabama we use it to store pool and barbecue stuff. Nothing we're interested in (edibles) will grow in it.

I grow in Florids year round. Have put in auto misting system and it realy cools thing down. Auto vent openers are a must.