A gallon or two of gas isn't going to get a motorhome all that far if one runs out of fuel. The only reason I would carry a gas can is to fill a portable generator or other equipment. I don't know why I would carry a portable generator with me when I have a perfectly good Onan one built into my motorhome connected to a big, easy to fill gas tank.
I'm not so sure about an empty gas can being safer than a full one. Gas vapor is explosive in the right concentration, while liquid gas is merely inflammable. Preferably neither one should be stored in an enclosed RV compartment in my opinion.