In the Guaymas area go over to the adjacent town of San Carlos. There are some beach areas you could tent on or go to the Totanaka rv park. They have a few areas for tents and good washrooms with laundry. Don't miss the Soggy Peso Bar and Grill.
In the Los Mochis area I would not stay at the Copper Canyon RV park in a tent. Noisy and too many people around. About 30 miles south on the beach is the Mr. Morros RV Park. Beautiful area and if they are not open stay on the beach just north of the park.
We travel this area in our Class A coach.
Good travels and enjoy the people.
Bob