Use SaveGame specifier in UPROPERTY macro, it's also available in blueprints in details of selected variable.
Then you need these two simple functions in C++:
TArray<uint8> ObjectSaver(UObject* SaveObject)
{
TArray<uint8> ObjectData;
if (!IsValid(SaveObject))
{
return ObjectData;
}
FMemoryWriter MemoryWriter(ObjectData, true);
MySaveGameArchive MyArchive(MemoryWriter);
SaveObject->Serialize(MyArchive);
return ObjectData;
}
and

void ObjectLoader(UObject* LoadObject, TArray<uint8> ObjectData)

{

`if (ObjectData.Num() <= 0) return;`



`FMemoryReader MemoryReader(ObjectData, true);`

`MySaveGameArchive MyArchive(MemoryReader);`

`LoadObject->Serialize(MyArchive);`

}

They uses special struct which you also need:

struct MySaveGameArchive : public FObjectAndNameAsStringProxyArchive

{

`MySaveGameArchive(FArchive& InInnerArchive)`

    `: FObjectAndNameAsStringProxyArchive(InInnerArchive, false)`

`{`

    `ArIsSaveGame = true;`

`}`

};

With this solution you don't need to expand your save structure each time you have new variable to save. Save structure only needs TArray<uint8> for storing the result of ObjectSaver function. Just add SaveGame flag to your new variables that you need to save.