Oh yeah smells awesome.
A few secrets to keeping them whole and nice throughout the process. Usually, when they're falling apart, it means they're overcooked. Which is fine if you're chopping it to go into a sauce or on top of a hamburger or something like that. But if you want to make whole chile relleno, then they mustn't be overcooked.
So to start, they can't be over-roasted in the first place. We went down to Central Market and were waiting as one of the dudes was roasting them, and when they were charred just enough, that's when we asked him to stop roasting them, and dumped them into our box. We've learned our lesson in the past, when they were over-roasted, and fell apart at home.
Second secret, once you get home, get them into a cold water bath so they don't keep cooking. We rinsed them in cold water and filled up the bag they were in, and even changed out the water once after the chiles had warmed it up significantly. Sitting in the water also helps the skin come off pretty easily. This batch had almost zero stubborn patches. Leaving a little char is fine, too, you just don't want too much of that chewy plasticky skin remaining.
And finally, when you slit them, you need to make the smallest incision you can at the top, and then slide the knife inside and cut that "seed pod" bit, or whatever it's called, at the top. That allows you to get the pithy chunk, plus most of the seeds, out without mangling the chile pepper. When you do it right, you're able to just pop that top bit out, with the slit being just barely more than the width of the blade. And then after you pop that bit out, you can rinse out the rest of the seeds (or leave some in if you like). At that point you might need to enlarge the slit further in order to stuff it, which is much better than having a huge gash down the side and needing to stitch it back together with a bunch of toothpicks.