I did a lot of this last year - 2-3 hour matches in high-80s to mid-90s and humid. It's great at building up your conditioning for hot and humid weather. Many of my regulars this year were away a lot so not so much tennis.
One thing that helps, I take two 1-liter Nalgene bottles, fill them almost full with water and freeze them for about 8 hours and bring them to the court. I also bring a smaller water bottle. The cold water helps on really hot days.
4 x IG Prestige MP, 70 cm, 376 grams, 386 SW, ALU Power @54, Prince Syn Gut 16 @58