I have never tent camped in DisneyWorld in the summer, but I did camp at Boy Scout National Jamboree this summer, and as everyone has probably read it was as hot or hotter there and we survived!! (100 actual temperature most days and 115 heat index most days, and about 85% humidity). (Please no comments about the accidents)
Hydrate, hydrate, hydrate!!! That's the first thing.
Make sure you have one of the newer tents where you can open all the windows and let air circulate, but the rain fly still keeps things dry inside.
Keep a fan blowing in the tent 24/7 to keep air moving and moisture down.
Make sure your tent is well waterproofed, cause even if it's hot, wet bedding never makes for a good night sleep.
Have some type of rain shelter that you can sit under in your chairs. You don't want to be stuck in your tent if it rains. This also keeps your tent drier as you can shuck the rain gear and the shoes under the shelter and walk into your tent in the dry.
Don't use sleeping bags. An air mattress, sheets, and a couple of blankets works better, so you can remove or add layers as necessary.
Take a nice cool shower, right before bed and go to bed with your head wet.
If all else fails, the comfort stations have blasting cold air conditioning, bring a chair into the comfort station and read a book till you cool off!!!!
Have fun!!
Carol