That's a pity about the zips and lack of fly vents. It might be worth trying to exchange your tent for one that does have better ventilation - it would save lugging a camp fan around and forking out for batteries and/or recharger.
Modifying it to include mesh and vents would be an option. However, in my mind, unless you could do it yourself, or if it's a you-beaut expensive tent, it's probably not worth the cost of doing so. Other more savvy campers may have other tips.
If all else fails, just keep everything off the tent walls as much as possible, and put something down on the floor to give you a dry "landing pad" to get in and out of bed.
Please don't feed the Goanna.