I've found that PREFIX alone is sometimes not enough. HTML::Mason, for example, would not install for me without all the added info. Here's the setup I use when I run perl Makefile.PL:

PREFIX=/home/tgi/usr/local \
INSTALLPRIVLIB=/home/tgi/usr/local/lib/perl5 \
INSTALLSCRIPT=/home/tgi/usr/local/bin \
INSTALLSITELIB=/home/tgi/usr/local/lib/perl5/site_perl \
INSTALLBIN=/usr/home/tgi/usr/local/bin \
INSTALLMAN1DIR=/home/tgi/usr/local/lib/perl5/man \
INSTALLMAN3DIR=/home/tgi/usr/local/lib/perl5/man/man3
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I have this saved in a file called popt (for perl options) and I just issue the command perl Makefile.PL `cat ~/popt`. I like to recreate the /usr hierarchy of a traditional perl installation, but that is not necessary.

To add modules to your search path you have a couple of options. You may be able to modify the enviroment on your server through an .htaccess file (if you are on an apache based system). On a mod_perl enabled server, you can use PerlSetEnv PERL5LIB /path/to/private/libraries/. Otherwise you are likely to be stuck adding a use lib qw(/path/to/modules /ya/path/to/modules); to each script.

TGI says moo

I do something similar in scripts that automate module installation. However, I use a longer list of variables:

$makefile_args =
  " INSTALLPRIVLIB=$prefix/usr/lib/perl5/5.6.0 " .
  " INSTALLARCHLIB=$prefix/usr/lib/perl5/5.6.0/i386-linux " .
  " INSTALLSITELIB=$prefix/usr/lib/perl5/site_perl/5.6.0 " .
  " INSTALLSITEARCH=$prefix/usr/lib/perl5/site_perl/5.6.0/i386-linux " .
  " INSTALLBIN=$prefix/usr/bin " .
  " INSTALLSCRIPT=$prefix/usr/bin " .
  " INSTALLMAN1DIR=$prefix/usr/share/man/man1 " .
  " INSTALLMAN3DIR=$prefix/usr/share/man/man3 ";

All I do is set the $prefix. Voila! Modules where we want 'em!