Anything close is going to be hot. Lakes like Millerton and Pine flat have camping if the heat doesn't bother you.
There are a couple of casino's like
Chukchansi gold resort casino that has RV parking. Table mountain is another but allows those at 18 to gamble IIRC.
The Harris Ranch might be a good choice to stay at.
Highway 41 takes you to Yosemite but above Bass Lake offers an escape from the heat.
Sierra Vista Byway is close by and offers a lot in the way of camping. The
Shaver Lake area also is high enough to beat the heat. A few private camps offer full hookups. Some of the members got together for a forum meet up that way a few years back and I wrote about it here along with other trips in the area:
Sportsmobile 4×4 Adventures
I'm not too sure about stealth camping in Fresno. Enjoy the trip and eclipse