Nothing left in a vehicle, unless the vehicle itself is in a secured location. And for the record, parking garages and the like are not 'secured locations'.
I've got a "truck gun" but it doesn't stay in the truck and I don't have it in the truck very often. When I'm in the vehicle my EDC stays on my waistband.
If you can carry in a way you can draw your gun while sitting belted in, and then practice it and always leave it on you. Appendix or a hip carry is comfortable in your car with some good practice draws are perfect for this. I think it's the best option