Thanks everyone for the additional suggestions! I changed the slic3r settings I was using and started with the high_quality_alt.ini this time, which apparently has a smaller layer height of .15, and it has a perimeter setting of 5. I put a space heater in the room (though I’m in San Diego and it’s been warm during the days when I’ve been printing), and I added plenty of brim, in addition to continuing to use a box over the printer with blankets on top of it. Unfortunately, it still has cracks 
It’s printing right now and already I can see the cracks already, but I’ll take a picture when it’s done. I could try getting a heat lamp as well since I need to print more of these parts. Sounds like I should also get some PLA to try.