First choice is to avoid leaving the dogs in the RV in hot weather but when we cannot avoid it - we use the generator with AC on BUT also have a 12V fan that we set down at dog level and leave it running. If for any reason the AC or generator stop, there is still lots of air moving via the 12v fan which helps some. And of course we leave plenty of water available.
Not ideal but for those QUICK shopping needs is the best we can do. Given a choice, one of stays in the RV with the furkids but a solo traveler does not have that option. Shop early in the day before tempos get too warm if you can. Good luck!