Only protection I'm aware of is for travelling through the state, not residing there even if for a couple of days. I travel regularly through SC from Georgia to NC and I contacted the SC DPS and got them to tell me how to travel through. Their instruction was "loaded or unloaded in the center console or glove compartment"
I'm not a lawyer and neither was the person on the other end of the phone, and each LEO interprets laws differently so take this information with a huge amount of caution. Also, do not speed in SC . If you are pulled over you will either have to appear or have a lawyer appear for you, you cannot just mail in the payment for a fine you incur. Plus, getting stopped could lead to a search should there be probable cause. I would just refuse a search as is my right, but then again I'm an onery bastard with that sort of thing. I would be polite and refuse a search, and they can bring as many supervisors as they want out and I'll still refuse the search. Oh, but I absolutely would inform the officer that I have my weapon in the car if asked. Do NOT lie about that as in SC you must inform LEO that you have a weapon.
Probably didn't help much, but sounds like you may need to leave you gun at home for this trip.