I have looked into auxiliary tanks and find the units costly. ($1,000 up for diesel). If you go with the above auxiliary tank nozzle you need to be careful of clearance with the trailer. Many states have laws on how you can feed fuel to the regular fuel tank. A simple gravity feed with an on/off switch is outlawed in many states and is very dangerous. An auto cut-off is the most reliable and is more dollars. The economies were not there for me. You also need to consider the weight of the tank with fuel as you may exceed the trucks weight capacity. Fuel is heavy. I have had to stop as much as three times in a day and it is a royal pain. Good luck.