The Nissan charging cable (called an "EVSE" as the charger is built into the car) isn't necessarily designed for constant exposure to the elements, and it isn't designed to be submerged in water, so your plan to leave it inside is good. You can cut a 12' 2x4 to sit under the door (flat), with a gap in it for the cable. You'd also have to cut a lock hole or two in the door track so it can be locked in that position. One problem with that, though, is it leaves gaps at the top of the door where it meets the garage wall, so wind and bugs can get inside.
2013 "Brilliant Silver" SV with Premium and no QC, a 2009 Vectrix VX-1 W/18 Leaf modules, and 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.