i prefer to just have a 'templates' subdirectory in each application's directory that contains the templates and use CVS to let the designers tweak them. then i'm the only one who can update the production site and i only do so after testing on a staging site. that will prevent the designers from ever really screwing up something production. when you first try to teach your designers how to use CVS, they may kick and scream a bit and don't be alarmed if blood streams out of their eyes and ears, but eventually they'll usually manage to understand enough to do a basic 'cvs commit' and 'cvs update'.
however you do it, i'd also recommend having a function somewhere in a common library that lets you just call it like my $template = template("foo_template.tmpl") and returns the loaded HTML::Template object with all the options you want and with the template file from whatever template directory you've settled on. this will prevent you from accidently forgetting to add 'die_on_bad_params' or 'loop_context_vars' every time (if you want them) and it makes it easier if you change your mind on where your templates live later on.