Even on a commercial semi truck, auxiliary fuel like gasoline is allowed, up to 8 gallons, with no hazmat labeling or CDL hazmat endorsement. Even 100 lbs of propane. The gas only has to be in DOT approved fuel cans like the plastic Rotopax ones I mentioned. That is 50 state legal. I have two of them, full of fuel, riding in a side box on my semi at all times for a portable generator on the frame rail of my semi truck. 8 gallons, at least, of gasoline in approved containers securely stored will meet any regulatory stuff. Over and above that may or may not require labeling depending on state.