That's a good question, mine are on different sides of the vehicle; is your vehicle petrol or diesel? If it's petrol I would also want to know where the fuel tank vents, some vent through the cap and some have a breather pipe. As you will have a naked flame when running on gas I would be VERY careful if it's a petrol engine... even diesel trucks have a warning lable saying "Turn off night heater 3mins before filling fuel tanks" to give it time to cool down.