That is correct. There are 3 ways to leave the firearm in the vehicle while on school property.
(b) It is a defense to a prosecution under subsection (a) that:
(1) the person is permitted to legally possess the firearm; and
(2) the firearm is:
(A) locked in the trunk of the person’s motor vehicle;
(B) kept in the glove compartment of the person’s locked motor vehicle; or
(C) stored out of plain sight in the person’s locked motor vehicle.
(c) A person who is permitted to legally possess a firearm and who knowingly, intentionally, or recklessly leaves the firearm in plain view in a motor vehicle that is parked in a school parking lot commits a Class A misdemeanor.
Question: would being covered completely by, say, a towel or gym bag count as out of plain sight?