# install bash for the linux-experience (and some scripts)
pkg install bash libiconv coreutils

# download burp (fix the version!), extract
curl "http://softlayer-ams.dl.sourceforge.net/project/burp/burp-1.4.34/burp-1.4.34.tar.bz2" > burp-1.4.34.tar.bz2
file burp-1.4.34.tar.bz2 
tar xf burp-1.4.34.tar.bz2 
cd burp-1.4.34
# install dependencies
pkg install openssl librsync perl5 gmake
# configure and install
# add '--disable-ipv6' if you do not have ipv6 properly configured!
# -- https://github.com/grke/burp/issues/182
./configure --prefix=/usr/local --sbindir=/usr/local/sbin LDFLAGS="-L/usr/local/lib" --sysconfdir=/etc/burp
gmake
gmake install
# replace 'date' in timer_script, as freebsds' date does not work as linux'
sed -i ".bak" "s,date ,/usr/local/bin/gdate ,g" /etc/burp/timer_script

Eventually set ca_burp_ca = /usr/local/sbin/burp_ca in /etc/burp/burp-server.conf

# run burp-server in foreground to see what happens (CA is generated)
/usr/local/sbin/burp -c /etc/burp/burp-server.conf -F

Create a really simple startup-script /usr/local/etc/rc.d/burp

#!/bin/sh

/usr/local/sbin/burp -c /etc/burp/burp-server.conf &
exit 0

Updated: 2015-04-09: add date-replacement with sed