Oz - congrats on the harvest of fresh veggies!
Okay, growing tomatoes upside down is a pipe dream. Simple logic would indicate the impossibility of the design as plants always grow towards the sunlight. Upside down planters are an exercise in futility. I've never seen it successfully done, except on television of course. (upside down planters are my pet peeve)
Grow tomatoes traditionally and sooner or later you will find the variety that works well in your climate.
When I was just getting into gardening, I actually had a successful experience with 3 upside down tomato plants. The plant will basically grow in a "U" shape, but when the tomatoes get larger, the weight will pull them down a bit. That said, they did not have the yields of my in-ground tomato plants, but I can't complain. Cherry or grape tomatoes do best in this kind of setting as the fruit isn't so large as to pull the roots right out of the planter.
You have to start the plants right-side-up and wait until they are a few inches tall. Then you poke them through the hole in the bottom of a hanging planter. The hole needs to be at least the circumfrence one would expect the stalk of the adult plant to be. (I used coffee filters to prevent the baby plants from slipping all the way through and to keep the dirt in. Then fill with dirt and water daily so that the water runs out the bottom of the planter.
Not too hard... but not practical if you have ground space where they could be planted instead.