- Yikes..why are you in Indiana and Kentucky for 3 summer months? If it's to visit the family, plan next year to do it in the fall.
- try to get a shady campsite
- get a site that has mid-day shade on your refrigerator
- get a site so you're not facing the sun in your motorhome with that big windshield
- keep your shades drawn
- Run the air conditioner (which in those temps, you probably already do)
- Leave vents cracked open
- Minimize your stove/oven cooking - plan 'cool' meals. When you do cook, turn on your exhaust fan, don't use a crockpot (or else plug it in outside during the day)
- Take cooler, shorter showers, dry the shower walls; hang wet towels over a lawn chair outside to dry
- don't use your washer/dryer if you have one
- in the morning, pull your mattress away from the wall a few inches to let the condensation dry out
If you have problems after doing all of the above, you'll just have to buy that dehumidifier. Good luck!