Instructions
Obtain a Tanker by accepting the "Tanker Commander" mission from Catalina. Begin the mission by getting inside the Tanker cab and connecting to the trailer. Avoid the pursuing vehicles as you drive the Tanker to Flint County. Complete the mission by arriving safely at RS Haul.
Get a Linerunner by going to the Ocean Docks in Los Santos. Locate one of these semis roaming the streets around the area. Throw the driver out and claim it for your own.
Go to Angel Pine to find a Roadtrain. Locate the Ammunation building, then head northeast across the street. A Roadtrain will be at the sawmill.