If you're in a state that says you can't have a loaded gun inside your vehicle, chances are they don't want you loading it to defend yourself. They want you to call the police and wait 15 minutes, tell the perp timeout and hope for the best. I was sleeping in a hotel parking lot in Ohio back in 2019. Someone tried to break into one of the side toolbox cabinets. They basically tried them all to see if any padlocks were unlocked. I couldn't see outside, which I felt was a disadvantage, but I can tell by the sound what they were doing. I sat inside quiet with my pistol in hand. I didn't want confrontation, especially in my underwear, and they really weren't causing any real harm. But if they had gotten the main door open, they would have gotten a surprise for sure, and that was my only real advantage. Didn't get much more sleep that night.
Sometimes you can't always take the firearm with you, so you have to leave it in vehicle. Or if you have 15 firearms, it would be very silly to carry all of them with you all the time. I understand your concern. I leave mine locked and hidden as best I can. My van is also manual transmission, so chances are very low it will get stolen.