In that case, I'd get a Tesla wall connector and mount it to an outside wall of your shed/garage/house or other building.
Tesla wall connector and Tesla Superchargers are safe to plug in and use in heavy rains. 
I don't know it it's necessary but I will unplug the car during nearby thunderstorms, just to be on the safe side. This goes whether car is in attached garage or sitting outside. I have experience with direct strikes of lightning and don't want to chance burning out my onboard charger.