Bob:
I didn't ask. I have found, in my 30 years as a plumbing & electric contractor, when you start asking questons, you get all kinds of answers, whether the person you ask really knows the correct answer or not. I don't have any placards of any kind on the tank so no one knows if it's solvent, gas, diesel or whatever.
I just put it behind my pickup, pulled it to town (Oklahoma City, OK) filled it up & pulled it home. Matter of fact, I pulled it to my business, parked out front for a while, then went home. I never really gave the transportion thing a thought, just build it & use it.
This is the same tank that I put in the back of my pickup, filled it with gas (110 gal), then headed for OSH this past summer. Gasoline is cheaper in OK than in a lot of other states.
I waited til I got to OSH to start using out of it so I'd know where I wanted to make the most use of it. Pulling a 38' 5th wheel with a 3/4 ton GMC at 6 mpg, it didn't take too long to empty it.
You could put a receiver hitch on your car & get/build a small carrier to slide into it. That would keep the fumes out of the vehicle. Sound like you don't really plan to haul much gas at a time anyway. You might even find a junked 20 or so gal weed sprayer that the tank is still good but the pump & stuff is shot. Make sure the plastic is compatible, but then again, gas "cans" are plastic.
The reason I have the 110 gallon tank is I live on an airpark & have my own hangar. I don't have to answer to any FBO or............. I don't see any difference in storing a 110 gal tank in there, than 3 airplanes & a couple of vehicles with full tanks of fuel.
Keep in mind, all this advice is worth just exactly what you paid for it.
Marshall Alexander