I am sure that there is an easier way to do this, but here's what I did...

I created an installation USB stick and installed 14.1 to an external USB drive. The partitions of the external drive are

/dev/sdc1 /boot
/dev/sdc2 swap
/dev/sdc3 /

After I installed I told setup to install lilo on my usb drive but that did not work. Everything installed, but lilo did not so I cannot boot. Crap!

So then I booted into the installation USB again and went through the whole install again to the external USB. This time I told it to create a bootable USB stick. It said that it did, but when I try to boot it doesn't even see it. Crap!

Now, how do I either

1. Make the external USB bootable so that I can boot directly from it, or
2. Crate a bootable USB stick that I can use to boot the external USB drive?

I hope all of this makes any sense. TIA!

If your booting the usb on an uefi system then:
Use Slackware 64 and usb partitioned in gpt format
The first partition on the usb needs to be type ef00, formated as fat32, and mounted at /boot/efi (the installer will take care of the mount points if booted in uefi mode).
use either elilo or grub2 for boot loader

The first time you installed probably your internal hard disk was known as /dev/sda, the USB stick as /dev/sdb and the external hard disk as /dev/sdc.

But then, after you remove the USB stick and reboot the external hard disk becomes /dev/hdb.

So label your partitions by UUID or LABEL in /etc/fstab and /etc/lilo.conf.

Also, as an external hard disk needs some time to spin, you will need to set in /etc/lilo.conf: to allow 15 seconds to the root partition for being readable.

To know the UUIDs you can use for instance.

man fstab and man lilo.conf to know more

I assume mistakes in naming. Be sure that you correct the boot order in hard drive to match the desired drive.