Thank you for all of the advice and encouragement you've offered over the past couple of days. Y'all offered some great ideas, and even better support; so, thank you! I joked with someone that "this too shall pass..." is on repeat in my thoughts these days, and I have to believe that it's true.
After lots of reading (your comments, parenting articles, etc.) and many discussions, Jeramie and I have decided that we are going to go with the "his room is his crib" viewpoint. Just as I had to give up the power struggle of forcing Ethan to eat, I also have to realize that I cannot force him to sleep.
What I can do, though, is make his room a safe place that invites rest. For us, this has meant removing all the things that could easily distract him from resting (large floor toys, fully accessible book shelf), and could put him in danger (the changing table). At first I felt bad about taking away his fun stuff, but this morning I realized we did it for the same reason Jeramie and I don't allow a TV or computer in our bedroom. Ethan has all morning, and an entire room of our house, dedicated to playing.
We are going to rearrange some things in his room and also create another acceptable space for him to rest. My good friend Jen calls it the "cozy corner" and I'm pretty fond of that name, as well. Ever since Ethan has been old enough to understand choices, we've allowed him to make them. For him, we've found that it helps to eliminate these power struggles and gives him a sense of control. We've decided to make nap/rest time no different. It really does not matter to me if he wants to sleep in a beanbag on the floor, or in his bed. Both are perfectly acceptable, and we'll all be less frustrated for realizing that.
I'm also not fully convinced that Ethan is in need of a nap anymore. In a week's time (half of which he was still in the crib) he has taken, maybe, two full naps. We went through this a couple of months back, but I knew he was still in desperate need of sleep. Back then, when he didn't nap in the afternoon, if affected his mood and he would sleep horribly that night. This week, he's had no trouble sleeping at night (even in the twin bed). We've been putting him down around 8:00 and he's asleep by 8:15, sleeping beautifully all night long, and his demeanor is unchanged on those no-nap afternoons.
If that's the case - if he really is trying to give up his nap - then I surely can't impose sleep on him, but I can still require that he has a period of quiet rest time in his room. We were already offering him book choices before we moved him out of the crib, and we continue to do so now. If he chooses not to sleep, then at least he has acceptable, alternative options.
So far (yesterday and today) this has worked really well. I can hear him over the monitor moving around his room, but it's often interrupted by 15-20 minute spurts of inactivity. I imagine that he's looking at a book, or maybe even nodding off, so I know he's resting and he's safe.
As long as I can guarantee those two things, I'll take it!