I agree with all the above in terms of heat fluctuations, avoiding fly strike, predators etc. In the UK outdoor pigs can attract rats to a property. Some posters from Europe have sadly lost their beloved piggies to heat stroke over a hot few days recently - it can happen so fast. I also hear vets in Oz are very expensive. The best way to avoid vet trips is to be able to keep a close eye on your piggies. The pleasure you get from observing their natural behaviours and interacting with them will also serve as a learning experience meaning that if any-pig should start to feel unwell you will notice differences in behaviour straight away.
For example: one of mine got a sharp grass seed stuck under her eyelid last week - I only picked her up to have a good look because I noticed that she was hiding away more in the day than she otherwise would have, and that her friend sniffed at her eye when she came out. They are in my kitchen so they are always in the background. The seed was quickly removed and antibiotics/eye lubricant/painkiller have sorted the problem. If I hadn't spotted it the same day it could have been a lot worse - potentially losing the sight in that eye or even needing to have the eye removed which would have been much more expensive.
This is not to say that outdoor pigs are always 'out of sight, out of mind' but they hide illness very well and it can be hard to spot how they behave when they think you're not looking. Sometimes the first indication that a pig is poorly is when the under-pig starts to challenge for dominance. They can tell!
Put a bit of lino down on the floor and then do your C&C on top as double protection. Consider the fleece-on-pee-pad option for bedding (or fleece-zorb-fleece which has worked very well for us) and you can knock up smaller versions for high-pee areas which can be switched out every day. I find the only problem smell is urine which is breaking down and smelling strong - the poops don't smell and are easy to pick up - some people just hoover them up when they have dried out! My old boar has a lovely smell - a bit like a horse I suppose - warm fur and hay.
One last thing - and just from my personal experience - because of my unique set up (and the kids being teenagers now) some of my pigs can safely go in and out of the backdoor at will. You'd think they would be outside all the time because "they're animals" but no. George stays inside all day unless I physically put him out - then he has a sniff round and comes back in. Flora goes out a few times - spends 5 or 10 minutes out there and then returns. My previous pigs have been the same... they LIKE it indoors and it's where they prefer to hang out. Things like fleeces and snuggle tunnels have been a recent addition to our house and it surprised me to see how much they love to lounge on soft-furnishings (again I was thinking "they're animals - animals don't have furniture!") I've always seen pics of pigs on soft pads or hammocks and thought they'd just been posed there but it turns out they like to be comfy. I mean - why was I so surprised!
Bring them in - you'll love it!
. Lots of people have inside piggie and they don’t damage the floor as long as you use the correct protection under the cage. Or you could set it up on top of a table. Good luck with bringing them inside. I think they would be better off especially as it gets so hot where you live. 
