I have adjusted the dCorePlus images to where when you burn a dCorePlus ISO to USB with dd, you can boot with that USB and then install dCore-usbinstall and run it on that same USB since the USB will have nothing mounted to it. The standard dCore ISOs when dd'd to a USB already did not keep the USB mounted after boot. So basically use dd to install an ISO to USB, in a root terminal do below if your USB is /dev/sdc and dCorePlus-xenial.iso is in the current directory. The dCore*.iso port can be downloaded and ISO-to-USB installed from any modern Linux distribution:
dd if=dCorePlus-xenial.iso of=/dev/sdc bs=4M
Be very sure you are specifying the right device or the entire drive will be wiped.
A way to find what /dev/sd* devices are USB can be done with the below command:
file /dev/disk/by-id/* | grep usb
Reboot using the newly ISO installed USB. Then import and load the package dCore-usbinstall from a non-root terminal:
Now run dCore-usbinstall from a root terminal. It should show the USB that was used to boot with as a choice to install to as part of the dCore-usbinstall process. Choose it, choose which dCore port you want to install to the USB, choose format with ext2. If you needed dCorePlus for the networking with the ISO installed USB, you will need to choose a dCorePlus port as your final frugal install at least for the initial importing of needed packages after first frugal boot.
If all went well, it should be that simple and now you can boot into the frugal installed USB. The TCE directory will be at the base directory of the USB and after booted should be ready to start importing packages. Best to use the RAM=TRUE option in /etc/sysconfig/sceconfg, or to use the -r option with sce-import as it will save wear on the USB. I wrote this in simple how to format for new users that may want to try dCore without burning CDs or messing with their hard drive OS install.