CPAN::Mini::Inject works quite well. It has a somewhat strange array of command line options, but they are well explained and easy to understand (just hard to remember).

The biggest hurdle to get a local CPAN mirror going these days is the regretable descission of some (not top be named here) people regarding the topic "Mirrors are a thing of the past, we'll do everything in our power to curtail the use of CPAN mirrors". That has unfortunately caused the cpan shell to have a somewhat worse support for local mirrors.

It's been some time since i last my local mirror, but it boiled down to having extra steps to configure the cpan shell, and running (if i remember correctly) into problems with signatures. In that instance, i ended up running a patched version of the cpan shell that disabled some security checks...