From SC gun laws:
It is unlawful to carry about the person a handgun concealed or
unconcealed except as follows:
(snip)
Any person in a vehicle where the handgun is secured in a closed glove
compartment, closed console or closed trunk. The handgun may be
loaded.
The law is specific: closed glove compartment, closed console, or closed trunk. I don't think a judge will see "fastened bag" in the text of the law.
Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote. NRA CSSA GOA 2AF CCRKBA / Tactical Pistol Instructor