I live in the CA. It still get around 100 F to 115 F. I think I found a way to keep my diapers cool while outside. This will work for Disposable diapers cloth or plastic back, Pull up & cloth diapers.
1 First you need to buy cloth inserts something like Diaper Booster cut a hole in the back side of cloth insert.
2 Crush 4 or 5 ice cube or more. Put it inside the Cloth diaper insert. spread inside the Cloth insert front to back evenly. My guess if you use just cloth diapers the outer most side of the cloth diaper next to the plastic pants would be best. (disposable Pull ups you might want to keep between the adsorbent part of the pull ups.)
3 Put the ice side of the cloth insert facing the diaper and the thick side cloth insert facing your skin. Or if you use a cloth diaper have ice face the plastic pants.
4 Then put the diaper on.
As the ice melts it absorb into the insert and diaper and keep your diaper area cool. (Note If you are a heavy wetter. You might want to use more ice. Because wetting can make it melt faster.
Reason why you don't want to use ice directly inside the disposable diapers or disposable diaper inserts. It will rip disposable diapers and you have to deal with the gel.
You do not want to just put it directly into the cloth diapers next to your skin. It will get your skin super cold. That why you use a cloth insert to put the ice.
I know it a strange trick but it works for me. It last about 2 maybe 3 hours.