Remember, I did note in the WIKI that putting plenty of cardboard down helps and that if you hold tray and concentrate on rollering, chances are you'll spill it. Put it down. Admit it, you ignored that bit didn't you.
If weather makes it difficult to do big areas, you can always do subsequent coats on seperate panels, as and when. Awkward areas can be done with sponge brushes or in some cases, a small narrow ordinary brush. You generally have to remove doors, one at a time, to fully get to all areas but you can get the main body paint on long before that. I tend to see any pre-winter touch up as the equivalent of waterproofing a boat hull now.
Steps need to be painted FIRST thing in the day and ideally don't fully close a door until 24 hours later so paint is at least cured unless you have some heat to dry it faster - otherwise door rubbers may mark the paint. The body needs far more coats (generally) than small edges and trim which aren't seen so much and exposed to the ravages of the road. If you do touch up later, always try to do a panel area up to seam lines rather than small areas that will leave tell-tale signs that you've been at work.
More bugs about now, so a polythene sheet laid over tray masy help keep the perishers out in between roller replenishment - just an idea.