I don't blame Haywire at all. I, too, spend the extra bit for PT lumber for things I build, like the carryall box, since I don't have indoor storage for my equipment, and I want this stuff to last despite exposure to lots of wet.
He's also right about those little brackets being expensive (so I'm just as happy to have found another solution when I built my carryall box), but I'm sure they are just the right thing to have in certain circumstances.
BOB