So, to summarize, it appears that HTML::Mason, as build in the RPMForge repository won't install with the system Perl. So, I may be able to sue Perlbrew to make a new Perl installation that I can use with HTML::Mason.
This appears to mean that I'll also have to rebuild mod_perl using the new Perl installation that I create with Perlbrew. Not sure how to do that yet, but looking into it.
I wonder if those people who work on the Mason project or the RPMForge project might want to look into fixing this, if it can be.