My BM tree isn't big enough to produce fruit yet. But I have had Preto ripen here in KY. I realize the heat and humidity isn't quite the same here as what you get but we do get a fair amount of both. Some years we get a lot of rain, other summers temps are over 100F and very dry.
Although I have no experience with BM yet, my Preto has produced some excellent, fully ripe, fruits that didn't spoil here. It's been said to be almost identical in fruit quality as the BM. The flavor is beyond compare.
I wish you the best with your Black Madiera there in SE. TX.