welcome to the group, the corner slide down poles work ok, I cant remember ours slipping, and you can put them down later when you have flipped the top if yo have forgotten, but dont forget or it might flip.
when we traveled aust we had a fridge in the camper and a fridge in our rig and still didnt have enough room.
the 12 v kit, although we never had that option back when i ordered one, might be worth it, cos we had lots of battery problems, usually flat most of the time, and if we had a battery charger at the start of our trip then things might have been a lot better.
so think long and hard about it, especially if you are going to travel around aust and or do BIG trips. but I dont know much about them, so I hope you get great advice about them from this group.
so as far as the rear legs go, save weight and stay with the standard pole legs, they work ok.