Well as long as you have a proper carrier or a box that they'll be able to have fresh water and food for the whole trip.
Many people on this forum do what's called a piggie train........ they'll get a rescue piggie from say north literally miles and miles down south to their new owner
Post a thread and ask some advice, i've only ever rescued piggies and had them in the car for about 1 - 1 1/2hrs....... i couldn't help with the water side of it, so i had cucumber, cos lettuce, canteloupe, but then carrots etc.. for them i had i think 9 piggies if i remember right, it was ages ago :{
You'd need to make sure about the temp of your car, and make sure the sun doesn't shine down on them........ cause you're in WA i'd be waiting for a cooler day, you've had horrendous temps for ages :{
yea the temp is getting better now and is raining more so its good weather so far (touch wood)