Charging outside with weather conditions

Toyota recommends against an extension cord. If it is too late to get a normal Prius, use a heavy gauge wire 10/3 as an example.

www.amazon.com/dp/B000HEC2DW

Toyota also recommends a GFCI outlet, for example www.amazon.com/dp/B071WD4Z4T

Both are speced for 20 Amps, so your breaker should be too. Your actual charger will draw over 12 Amps for almost 6 hours, so the equipment has plenty of time to get hot with smaller wire.

The car end has many weather fail safes, the dangerous end is the normal plug. www.amazon.com/dp/B009RX5GI2
The large size may hold the bulge as well, but it won't provide ventilation.

 

I have been doing my charging outside on my driveway with stock OEM L1 charger even during winter in a few feet of snow on ground, but I worried about the charger brick being outside exposed to elements just like you. So, although I have GFCI outlet on outside wall, I have been using GFCI outlet inside of garage and connecting to the car parked next to garage. Yeah, I have a detached garage, but currently it is not in a shape to park a car inside. I think the charge unit is weather proof, but I don't know about leaving it snow. If I were you, I would put the charger brick and extension cord connector in a watertight box to protect it. Something like this would work, I think.

 

i've been charging in the elements for six years with no precautions and no problems

 

I can't comment on the long term but what I can say is the brick is weather proof (not waterproof), so if it rains, pours, you'll probably be fine, just don't want to leave the charger in standing water and the same goes with the plugs if you're using an extension cord.

If you're using an extension cord (with L1 charging) I would go with heavier gauge something like 12 gauge or larger if you're going 50 ft or more. If you're going with L2 probably would need something like 8 gauge.

I haven't had any problems with 12 gauge at L1 charging. My watt meter shows about 1,300 watt pull and does decrease if the sun beams down on the charge cord by about 20-30 watts. So I should expect slightly faster charging in the winter? (temperature coefficient...low temps, lower resistance)