Brazilian Chevrolet S10 with underbody CNG kit and roof-mounted spare wheel
Compressed Natural Gas is the most common gaseous fuel for street-legal motor vehicles in Brazil, and Liquid Petroleum Gas is actually outlawed for such use, and for some it's easier to retain the stock cargo space fitting the CNG cylinders under the body. This is quite usual for body-on-frame trucks such as the Chevrolet S10, with the cylinders installed where the spare wheel is originally located, yet only smaller ones would fit there. Usually the CNG cylinders are placed transversely, yet once in a while I see some with them mounted longitudinally. Such position would be more favorable for a vehicle with a longer wheelbase where the cylinders could be saddle-mounted in parallel with the frame rails, which wouldn't be much rocket-science considering how the stock fuel tank is positioned in parallel to the driver's side frame rail.