Download the script to /usr/local/sbin, and add a cron entry, as root, to run the script once per month, similar to:
59 00 1 * * /usr/local/sbin/300.statistics
The following variables can be set in /etc/rc.conf.local to enable the statistics, as well as fine tune various parts of it:
* monthly_statistics_enable="YES"
* monthly_statistics_report_devices="YES" After downloading, run it once initially.