You can be suffering from a number of small problems that are adding up on you on hot days.
With an older RV, you must keep your COACH battery relatively NEW and full of water and fully charged.
Your Air Conditioner will age and eventually, it will draw several AMPS more current to start up and to run, so keep the air filter clean and you could even get up on the roof and clean the coils for better airflow.
Next, on those really HOT days, you should take precautions to only use your necessary appliances and make sure you unplug the things that are not necessary during the peak periods of heat during the day. Read my article on How to Keep Cool in your RV for tips.
Many people don't realize that breakers that kick out often can eventually weaken ad not be able to handle the load they could when new, so consider replacing that MAIN breaker to get a couple of more Amps during these peak periods.