Need help building mfsBSD

Every so often I attempt to build a version of mfsBSD which is usable on my system. The ones available are either for amd-64 or no longer supported versions of FreeBSD.

The scripts for building an image are here

and the instructions look relatively simple, but I'm damned if I can get anything to work....

I'm not sure if I need to download and mount an ISO image of the distribution I want to build or if I can use my current installation. Either way I end up going round in circles and not getting anywhere.

If anyone can help, I would very much appreciate it