I prefer to manage Red Hat with RPM-- the first step when I find a new module I'd like to install is to see if there's an RPM of that module. Here's a strategy:

(1) Do an (up2date install perl-Crypt-RSA) to see if Red Hat Network already has it packaged.

(2) Google for "perl-Crypt-RSA rpm" for some ideas if this is commonly packaged by third-parties.

(3) Download the CPAN tarball and use a cpan2rpm converter script to make a .src.rpm for it. This .src.rpm will have all of the build-requires fields properly set. Then rebuild to get the .noarch.rpm or .i386.rpm or whatever.

Every once in a while, someone proposes an all-CPAN RPM repository, but I've yet to see anyone stick to such a project. Since Red Hat is a python-favoring distribution, this is not a big surprise.

This may seem like a pain to manage, but it makes your Perl configuration easily duplicatable on other machines, and eases your management of upgrades of the whole system.