I did a similar thing for some outside lighting, where I used a WeMo outlet that did not fit under the weatherproof cover. I used draftboard, and it held up for years.
My concern with using the finger joint was the box coming apart from the wall, so I made a slot, and a piece that fit through the slot, then a spacer to glue to fill that distance between the wall and the piece that went through the hole…. (sorry running on a few hours of sleep right now)
It makes complete sense in my head but here are some pictures, and maybe it could be pieced together…
The charger cord fits in that cut out, and is sheltered from the rain. I thought about making the box more narrow but then it wouldn’t create as much of an umbrella.
In retrospect I should’ve engraved an umbrella over the electrical outlet.
The live end just hooks into the charger like a gas pump when not in use, the wire just stays on the floor as I am too lazy to wind it up each time. There has to be a more elegant solution than what I am doing with the slack wire that accounts for me not wanting to loop the wire each time, like a pulley that retracts.
Is there anything overhead? I have a simple bungie cord arrangement suspending the cord overhead and just loop the end over the hook when it’s not in use. Works great, and keeps my floor clear!
It’s the overhang of the garage outside. So I think I would need some other kind of set up because it’s at the very corner of the garage, and it would plug in at the other corner of the garage door. I don’t think my wife would appreciate the wire dangling over the entire garage length.