It sounds like they have to investigate existing, or set up some micro climates of their own. Perhaps grow Seminole Pumpkins on the edges of the garden – over trellises, and grow more tender crops in the shadow of them. If you attempt to grow in a hot, humid climate, the rule is to always protect plants on the western side, and attempt to grow under canopy. But allow for air circulation too, or mould will wipe everything out.

Find some die-hard, native species as your sacrificial crops (they don’t have to be edibles, but bonus if they help fix nitrogen) and grow them on the western side. In my experience growing in hot and sometimes humid conditions during summer – autumn is where we get the most productive growth. Summer just fries everything. Perennials are also better than annuals, because they mope during the heat of summer, but pick up growth quickly when autumn arrives. All my annuals died once planted in spring and summer cooks them. And if I plant in autumn, sometimes the cold will kill the warmer climate crops. Perennials fill that niche perfectly.

If they are going to try growing watermelons, I’d plant them underneath a small tree or shrub, where the roots can be shaded, while their vines meander to the top in order to bloom. Of course you might need to net them, for support as they grow. Beats paying $50 for a watermelon though. I wonder if sweet potato would work, because you can eat the new shoots of the leaves, before the tubers are ready? That’s if they can’t find yams.