Well, we are getting into stuff here that i am no expert on, for sure, but I would be sort of worried about an extension cord outside in bad weather. I think there are "outdoor cords" so you might check into them. We had an extension cord once--the big orange ones that are supposed to be sturdy, to run power tools, etc, on, and hubby left it stretched out inthe yard where he had been working, as he intended to work there again the next day. He left the one end plugged into the plug-in in the garage, and the other end just laying in the grass. That night, it rained, and the water got into the end of the cord, burned out the cord, and ran all the way to the plug-in, burning it out, also. A friend of ours that is an electrician said we were lucky it didn't burn the house down.
What kind of a waterer do you have? Doesn't seem likely it would spill. Maybe you could set it in a corner and brace it a bit with a wire loop that you drop over it, nailed to the wall on each side of the waterer. I think I would want my feed inside, also, so it doesn't get damp and mouldy, which would be very bad for the chickens. If you just have 4 or 5 hens, just one of the little round "chick feeders" that screw onto a half gallon jar would hold feed for 2 or 3 days, wouldn't it?
Hopefully someone else here will join with some advice from their experience.