The M1 Super 90 and a full bandoleer of Brenneke slugs and 000 buck is in the vehicle at all times...
You may find as I did that the vibration and bouncing about resulting from extended carry in a vehicle eventually loosens the wads in Brenneke slugs, offering less than usual accuracy. Those in my circle who continue to use them generally swap theirs out at specified periods, from weekly to monthly, depending on preference and experience.
I've also noted the possibility of tearing or shearing of the relatively thin rims of Brenneke slugs in autoloaders, and at least potentially in a pumpgun with a heavy-handed operator. Even the shell stops of the magazine ding up the rims of the Brenneke rounds, requiring frequent inspection, at least.
They do work swell in double guns and singlebarrelled shotguns, and in those weapons increase the odds of getting the job done with a single, well-placed shot. And for a gun that rests in a less severe opereating enviornment, they're just fine.
But I use other slugs in the shotguns carried aboard my car, truck and motorbike. The triple-ought buck loads you use should do just fine, though I go for something with a bit less flash at night. Different guns have differing preferences so far as shot loads go, and my old 870 tends to prefer 20-pellet #1 buck loads. But either triple-0 or reduced recoil 8-pellet 00 buck loads are available, and are sometimes my choice as circumstances dictate.
That Brenneke slug remains a particular comfort as the first load up when travelling in bear country, though....