Hi Teri ... you have an issue there in Texas that I do not have here in Arizona, and that is humidity. I have had my ileo about a year longer than you have had yours (11/10/15 is my stomaversary LOL). You do have to be very aware of your electrolyte and sodium balance, and potassium.
I personally drink Powerade Zero, that helps keep the sugar intake low. I drink that all year round, but admit I do not do it as methodically in the winter (or at least what we call winter here in the Valley of the Sun). If you sweat a lot you are sweating out electrolytes, sodium and potassium and will definitely need to replace them.
So Powerade it up, lady :) ; Also be sure to hydrate very well because you do not have a colon any longer that is absorbing liquids into your body to hydrate it. You will know if your levels are getting low by the way you feel. And I think we all know that if you stop sweating you are dehydrated or getting there pretty darned fast.
So yes, load up on electrolytes through sports drinks, eat potassium-filled foods and hydrate until you cannot hydrate any more!
I am fortunate in that I am retired and if I have to get out I tend to make it earlier in the morning or later in the afternoon, but not in the hottest part of the day. I do not have the perspiration issue that you do, but it sounds like you can keep it under control!
Paula