I like Marquee Rentals in Austin. Ann is the person I always work with, but all of them are wonderful. They will be able to make great suggestions for you, they have EVERYTHING! They will also deliver. Call to reserve it now so that it will be available. The fans to provide cross ventilation will be great.. They have fans that do a mist of water.
http://www.marqueerents.com/
Having it later in the day with lots of cold drinks will help. Slice lots of watermelon and have it really cold in a cooler that people can eat it through out the whole party. Also lots of grapes. I always had a 3 gallon beverage cooler of water and a 3 gallon beverage cooler of lemonade at our summer events..Have plastic cups that people can write their names on so there will not be lots of waste.
We have lots of June and July Birthdays, So I completely understand this situation.