The NANO_LABEL variable needs to be set in order for the image to be portable in the way I explained earlier in this thread. I was able to completely omit the NANO_DRIVE variable, setting just the NANO_LABEL variable and the system booted right up when I tried the both the regular sata or usb ports. I checked fstab entries, sure enough everything's called by the label passed to the variable.
It was very nice to discover that NanoBSD does that out of the box, instead of having to do custom patching
