Without Boot Camp, I tried using dd and that didn't work and just reformatting the USB drive to exFAT (FAT32 didn't seem to work, because the October 2018 update has a file over 4 GB, meanwhile I'm downloading April 2018).
It right away asked for the ISO and started downloading Windows support software, took forever, and then said there wasn't enough space on the partition (there was). My Boot Camp assistant seems to be having problems (first I get not enough space, 40 GB, etc.) which I fixed by making a partition using Disk Utility, but then I didn't get an option that others seem to get to Create a usb bootable drive for windows 7 or later.