I've installed 10.13.5 on an external USB drive clone, and then once everything is working okay, only then did I clone it back to my SATA internal drive. Reason I need to do it this way is if the upgrade fails, I want my computer to be unaffected so I can get back to work quickly and try again for another day.
In my case, I have to move my USB3 drive/enclosure and plug it into a USB2 port... only then was my High Sierra installation successful (can be seen by Clover, no KP, no hang in the middle of OSX upgrade, etc) When my enclosure was plugged into a USB3 port during installation/upgrade of HS, I encountered a lot of problems.