Looking good Bri, I would consider adding a fan too, a simple pc case fan powered by a redundant phone charger is good enough for most folk.
Imho Its best to keep the air moving inside as then it can transfer the heat or cold from their respective radiators to the fermenting vessels much more effectively and efficiently. The air inside your fridge is the medium by which temperature change is effected in the brews. so relying on convection alone to move the air may not be prudent
Look at the top end domestic fridges and most of the commercial fridges, they generally contain fans for just this reason. while some have fans cleverly wired up with the controller to only come on when heating or cooling is on, i simply run mine off the fridge main power in so its on 24/7 with the fridge,
Just dont epoxy the fan to the fridge shell like i did DOH!! as after a few years the fan may die, and if epoxied to the thin plastic shell you may find yourself gutting fan#1 to become the mount for fan #2..
also when it comes to threading heater flex, fan power and probes through the drain hole. the flex supplied with the tube heaters is quite bulky, but as it only demands 40-60w of power similar to an incandescent light bulb, its perfectly safe and acceptable to rewire the tube heater with thinner lighting flex, and the cheapest bell/speaker wire going will be sufficient to carry the dc voltage to a pc fan..
cheers..