High Sierra won't install

Ok... Long winded post here. Hopefully I don't miss anything.

I have a late 2009 27 inch imac that I just replaced the dying HDD with a Samsung Evo 840, 250gb SSD. Hardware swap was easy.

I made a bootable usb stick for installing High Sierra. Booted up and selected to boot from USB.

Ran Disk Utility, selected the SSD, which was clearly visible, and erased everything on it, setting it to APFS and GUID.

Worked fine.

Starts to install and gets me to a screen that says simply "macOS could not be installed on your computer. An error occurred installing macOS." No error code or anything like that. Then the option is to "Quit the installer to restart your computer and try again."

Hit Restart and the computer gives the grey screen with the black apple and progress bar. Bar completes one round and goes around for a second shot.

This one gets to about 1/3 done and says "Installing: About 11 minutes remaining" and crashes back to the same error screen, "macOS could not be installed on your computer" and the only option is to Restart.

I've done this, on the off chance that it wasn't a loop, and so far it has been about 6 hours of the same.

Ideas?