Jengo
The Jengo Peccary (No Top) is a roofless, doorless 1963 military jeep that the FND uses to move troops. It is a common, quick SUV to steal and carries four people.
Quick transport over roads and dirt tracks with room for a squad. Being open, it gives you no cover from gunfire.
Ambush an FND patrol and take the jeep. Drive it to any vehicle pickup point to add it to your list. After that you can spawn it at pickup points instead of hunting for another one.
If you want a gun on the back, steal the Jengo Warden instead.