Could you "adapt" a roof bike rack to take your C-stands, or use one of those sealed aerodynamic roof containers to hold smaller stands, tripods, scrims, etc? Then take a folding footstool to be able to easily access the container?
I've thought of the top carrier for the car (Prius) as I know one photographer that uses one on their van. Problem is I would probably fumble the heavy Matthews stands and damage the car at some point as it is sloped over say a van.
The C-stands with the removable turtle base aren't that much of a problem in that the upright is just a pole and doesn't take much room so I can put three in the back seat easily. The bases are a bit much stacked. The problem is my flash units are too big (Circa 1990) in their large carrier cases that hold 5 heads. A new smaller head might be better as they weigh less and are half the size now, but not too crazy about tossing working gear. Sundry stuff like spools of 100' extension cords, snoots, barndoors, even a smoke machine, etc. make my packing a bit frustrating.
The Prius oddly has a hitch that I have used in the past to haul a motorcycle trailer. Gas mileage took a hit though from 45 to 22 mpg. A top carrier might affect it too. I think the newer ones have a bit more storage space, but can't beat it for location traveling, other than packing the thing tight with gear. Some small aerodynamic trailer with side-load compartments maybe that I could leave packed with the stands and lighting stuff in the locked compound.
Example, this one for some clothing outfit shot down inside a working gold mine took three C-stands and flash-heads, dishes and umbrellas, and 300' of extension cords for the lights. I had battery packs for the flash units, but I needed the modeling lights on as it was pitch dark down there and doing that kills the batteries. Was sort of creepy in there with only the kerosene light lit or her helmet headlamp on. People got claustrophobic otherwise so we had to add music too for distraction.
SG