Hy . You mentioned your tail lights, yes, there is a rubber seal  between each  tail light assembly and the  body of the car, Make sure it is in one piece. If not, you can make new ones with rubber material, even inner tubes( car tires) ...work good(if not able to find  the original seals or a piece of rubber big enough to  cut a  new seal )..., and make sure when  tightening those small  nuts, to do it in a cross pattern, as in bolting in lug nuts in a wheel, to make sure no water comes in. 
  About those bat cables, get a bean bag or something else and put the bat cables in it, those cables free  flying around the  trunk will chip off paint, you would be surprised to see how rust starts from  those little nicks and scratches,add humidity(hot summer/wet winter)... rust is not welcome in a Datto.
   Later____________________________ 
