May / June is hot in Mexico and in some areas a lot or the RV Parks are closed for the summer. Must check ahead of time with the park to make sure they will be open. Have been South of AZ in Mexico in May on the beach. On the beach can / may be OK but when you go inland the heat becomes overbearing and that is coming from someone who lives in AZ full-time. This time of the year I would make it easy on myself for a first trip and go to Rocky Point / Puerto Penasco or San Felipe. Both are easy drive (Rocky Point the easier of the two) and require NO Paperwork, only Mexican Insurance. Maybe Kino Bay but a harder drive but still a nice short summer location. Some of the Parks in Mazatlan close and depending on the location a bug problem (no-see-ums). Takes a few days to Mazatlan vs same day arrival for Rocky Point and San Felipe and easiest border crossing is Rocky Point. Just a little note, Rocky Point is some time referred to as Arizona's only Beach. If winter further South into Mexico would be best. Good luck and enjoy!
rocmoc n AZ/Fld/Baja