Which brand/type of rolled fondant will hold up to being refrigerated once it's covering a cake? Which one is best for humid and super hot weather? Also, what are the best ways to transport a cake in super hot weather?

Any fondant will hold up to refrigeration. The problem is the condensation that forms on it when you take it out. If you live in a humid climate, that can ruin your fondant decorations. If you're going to refrigerate a fondant-covered cake, put it in a box and wrap it airtight in plastic wrap. Let it come to room temp before you unwrap it. That way the condensation forms on the box, not on the cake. Albert Ulster makes a fondant called Massa Ticino Tropico that's great for hot, humid weather, but it's very expensive. In hot, or any other, weather I line my car trunk with non-skid mats and stack the tiers at the venue whenever possible.