Once in your truck, use the standard F4 menu to adjust your seat. You will notice that the "sliders" no longer stop at the usual boundaries, allowing for unlimited movement.
Because it removes limits, the camera can easily clip through cabin textures or the truck's external model if pushed too far. UNLIMITED CAMERA MOD - ETS2 1.43
Removes all barriers for seat positioning. You can move the camera to any point in the cabin, allowing for unique "sleeper berth" views or unconventional driving stances. Once in your truck, use the standard F4