If you do not have a Maine permit then you can OC in a vehicle unloaded and you can OC loaded anywhere else in the State that isn't posted as No Firearms Allowed. You can shoot on your property. Just please make sure you do so with safety in mind. Be aware of your backstop and what is beyond. Check with your town to make sure there is not a "No Discharge" ordinance which would prevent you from shooting on your property, and the State Preemption law DOES allow for towns to limit the discharge of firearms within city limits.