I can't say that I have ever seen anything like sunscald before. The sun must be pretty intense where you are. I wish I could say I've not seen a slug or a snail; they are the bane of my gardening existence. I am constantly picking them out of pots, off of plants, or evicting them from my greenhouse - they are such a pain!
It is so moist here that is impossible to eradicate them. At least where hornworms are concerned, if you cover/isolate the plants to keep the moths off of them, you don't have worms. In July and August most people here don't see fruit on tomato plants. Because of the heat, the plants don't continue to flower and set fruit. You just have to work at keeping the vines alive until fall when it cools off again. If you're lucky, you get tomatoes into the winter.