Yup, been doing it since 2012, rain, snow, sleet, etc, etc. but my hearingaids keep shorting out (I don't know why)
Rain, what's that?? Oh no, what is that stuff in the sky, it can't be!! Is this the mysterious stuff called RAIN??!! Yes, it's FINALLY Raining (November 27, 2017; put it in your calendars) in Anaheim, California!! Well, you guys would probably call it a sprinkle, or a drizzle, mist, maybe? Would you believe heavy dew? How about foggy condensation. Hey, we'll take whatever we can get, after Satan's Bad Breath of temperatures we have been getting for THANKSGIVING; new record high temperatures in most Socal cities!! .
One caution, the plug at the car is designed so that the power cables are connected before the sense cables, so power comes on after the plug is seated. If your 110 volt end is also in the rain, it is much less protected. Try to arrange it so you power the circuit after you have inserted the 110 volt plug, if wet.
interesting one here: Extension Cord Safety Seal - Green-H-EXT-301-GRN - The Home Depot Has an adjustable internal piece to prevent the connection pulling apart if tensioned.