Aldo, all you need to do is open carry if you are concerned. No need to lock it up.
In plain sight on the seat or dash will make you legal
As ranger04 pointed out, I would be concerned about the unpredictable car accident--usually the other driver's error that is out of my control
--or the eye-popping shock
of other motorists seeing a handgun out in the open on the dash.
In the case of the unpredictable accident while I have my gun in its IWB holster, I am not so sure that the local LEO in one of those 13 cities would not cite me with anything (despite me having my CCW permit, or with what Bruning has rendered as his legal opinion).
In the case of the reaction of other motorists, again I am not sure of the LEO's response to some motorist calling up 911 or the local LEO and making a case for me re "disturbing the peace" by having my gun in plain sight.
Personally, I just want to be able to carry concealed for self-defense where ever I am in NE (other than the posted and listed banned buildings, etc), and so I like Bruning's legal opinion. So, it will be interesting to see how those 13 cities handle it.