I have normally carried "primary" at 0300 to 0330, and use holsters that do not collapse when there is no weapon inside the holster. I have been able to draw, and re-holster, when seated inside every vehicle that I have owned, or have been issued, has been compatible with this, from compact cars such as the VW GTI and Honda Civic, to SUVs, to my present Toyota Tundra. Seat belt interference has never been a problem.
If your holster collapses after the weapon is drawn, well, get a better holster.
Unholstered handguns, loose inside a vehcle, become misguided missiles all too easily. Use a holster.
Carrying at 0400, or beyond, seems, to me, to be a tactical blunder. The concealment factor is high, but the accessibility factor is low.
For a specialized driving holster, well, cross-draw. Get a really, really good one, not cheap junk. Another driving rig solution is a shoulder holster. I live where it is tropical-hot/humid most of the year, so my carry time with shoulder rigs is limited, but my Andrews Monarch is excellent, for a secondary/tertiary weapon. Again, one gets what one pays for; cheap shoulder rigs tend to bring dissatisfaction.