To clarify what azredhawk posted:
The rule regarding keeping a loaded weapon in the glovebox requires a 2 step process to operate the firearm. Step one is opening the glovebox, step two is removal from a holster or a soft case. A holster that has an exposed trigger will not qualify as the second step since the weapon can be fired while in the holster.
Another option is with the mag loaded, but not inserted in the weapon. Then a holster or case is not required. Step one, open glovebox, step two insert mag into weapon.
As far as open carry on the seat, unless there is a map or other junk on the seat partially covering the weapon, it is legal to keep your loaded weapon on the seat; unless you are a jerk to the officer, then you may get some grief in return.
It is a bad idea to keep it on the dash and a worse idea to move to the dash during a traffic stop.