Thanks for the plug, Ridgerunner - your check is in the mail!

Seriously, OzarkEgghead, Ridgerunner is spot on with the advice you got, as usual. I brood my chicks outdoors too, but rather than use a heat lamp I do indeed prefer a heating pad draped over a cave. My first chicks were raised in the house and by 2 weeks old I was ready to throw them all out regardless of the unfinished coop, the sub-freezing temps and snow. By 5.5 weeks I did just that! Oy, the dust! The noise! The work! Life is so much easier now, and the chicks I raise are so much stronger than those! I'll give me a shameless self-plug here and offer this article for you to look at.
https://www.backyardchickens.com/a/yes-you-certainly-can-brood-chicks-outdoors As for RIR, I've only had 3 of them, all roos and all quite by accident....a sexing error at the hatchery led to them being identified incorrectly at the feed store where I got them. And I ain't smart enough to know the difference until that first long, curly tail feather and that jarring crow appear! Those birds are in the freezer. They were indeed aggressive toward us and toward the other birds they were raised with. Is that true for all RIRs? I don't know. I very much doubt it. I have a good friend who has them and she loves having them and has never had an issue. So there ya go - same breed or variety, different results. Most folks love their Golden Laced Wyandotts too, but I couldn't get rid of those 5 bullies fast enough. If one was picking on a chicken the other four had to come and join in, pummeling their victim without mercy in a warped game of gang-war that was totally beyond pecking order issues. So in each breed or variety, you can have a variety of different personalities. But I digress - again. Lazy Gardener has a good idea about the extension cord, if for nothing else for water. But as she said, if you choose to do that, make sure that you've used all sensible precautions. When I use one, my professional electrician husband about has apoplexy, but we found these plastic protectors at Walmart. They are bight orange (at least mine is...I've since seen blue as well) and when you get the plug of the appliance pushed into the end of the extension cord, the hard plastic protector snaps shut around the connection. It's sealed against moisture and pulling apart that way. Good luck with what ever you decide to do!