I'm in the middle of my first rear quarter panel replacement and so far the biggest hurdle has been previous repairs slowing things up. Someone has welded the outer gaurd to the inner gaurd making removal very difficult.
The hardest sections to make fit looks to be where the rear quarter meets the sill panel in the bottom corner of the door opening and re braising (brass stick welded) section at the top of the panel under the side vent.
Hot Rocket is dead right, I bought 4 spot weld bits for removing the hundreds of spot welds that hold them on. Get a short one and a long one at the very least. Just centre punch the middle of the weld and drill. As soon as you see a puff of rust dust you know you're through!!
Where the panel mates to the tail light housing is a bit hard to find the spot welds as they've been ground completely flush with the panel unlike all the others. I just pulled the panel out firmly so it stretched a bit and showed where the welds are.

Welding them back on should be quite easy apart from the tricky bits mentioned. Get 4 large panel locking pliers (vice grips) so you can hold the panel in place prior to welding it back up.

I reckon give it a go, you can't damage too much taking it off (make sure you get your new quarter first so you can see where to cut the old one around where it meets the sill panel) but if it gets too hard you can always take the new panel and the ute to a panel beater and get it done properly!

I hope that helps!