In MSCLoader 1.2.8+ there is a new method to store your saved stuff, based on feedback from other modders it brigs a unified save location for all mods into a single file.

Best part is you don't need to trash your current save system, instead of saving your current save to file, you can save and load it as byte[] array into this new save method.

bool testBool = false;
int testInt = 395352;
Vector3 testVector = new Vector3(34f, 0, 12.5f);
List<string> testList = new List<string>() { "test1", "test2", "test3" };
//OnSave
SaveLoad.WriteValue(this, "testBool", testBool);
SaveLoad.WriteValue(this, "testInt", testInt);
SaveLoad.WriteValue(this, "testVector", testVector);
SaveLoad.WriteValue(this, "testList", testList);

//OnLoad
bool readBool = SaveLoad.ReadValue<bool>(this, "testBool");
int readInt = SaveLoad.ReadValue<int>(this, "testInt");
Vector3 readVector = SaveLoad.ReadValue<Vector3>(this, "testVector");
List<string> readList = SaveLoad.ReadValueAsList<string>(this, "testList");

valueID - valueID needs to be uniqueID for your mod, you can read value stored under that ID using ReadValue methods

There is new method to serialize custom class int unified save file. To serialize your class just add in OnSave

SaveLoad.SerializeClass(this, myClassToSerialize, "mySerializedClass");

To deserialize your class just do in OnLoad

MyClass myClass = SaveLoad.DeserializeClass<MyClass>(this, "mySerializedClass");

In SerializeClass there is optional parameter to "encrypt" your data.
If you decide to do it you need to also set optional parameter to true in DeserializeClass

If you already have custom save method, you can also save that file into unified save file.
If your current save file is in binary format it's recommended to save it as byte[] array
Examples:

SaveLoad.WriteValue(this, "mySaveFile", myByteArray);

To Load it:

byte[] myByteArray = ReadValueAsArray<byte>(this, "mySaveFile");

SerializeSaveFile and DeserializeSaveFile methods, serializes file to custom .json file