I keep my kit in the bed of my pickup. Typically it has either a truck box (manual lock) or a tonneau cover (soft, ie, not secure). The tail gate doesn't have a lock. Makes it easy to take things out, but it also makes things easy to take out. I typically try to back up to a wall or light pole or something to act as an impediment to sticky fingers. The camera in the tailgate really helps.

My wife's car has it in her trunk, not accessible from the backseat, but works with a key fob.