Open carry is allowed in vehicles or on your person, without a permit (assuming you're not a convicted felon or whatever).
"Open" is not well-defined, but relatively lenient.
Concealed carry is allowed without a permit outside city limits while engaging in any lawful outdoor activity.
To carry a gun unloaded and concealed in the vehicle, just have it out of the "grabbable area". In a soft case, unloaded and under the truck seat should be fine.
Do you have a CCW permit from another state?