Run:

sa-update
wget http://daryl.dostech.ca/sa-update/sare/GPG.KEY
sa-update --import GPG.KEY

Add to root's crontab:

# Keep SpamAssassin stuff updated
00 2 * * 3 sa-update
15 2 * * 3 sa-update --channelfile /etc/spamassassin/sare-sa-update-channels.txt --gpgkey 856AA88A