The rubber strings can be problematic in very high temps. A friend was playing his fretted UBass at a festival 7 years ago. The day was 48degC (118 degF for you Americans) and even more in the tent. He kept tuning up, and up, and up and the strings were like licorice....... no matter how much he turned those tuning pegs the strings just kept stretching and were flat.
Oh yikes!
