plugin directory is /usr/lib/keepass2

for plugins to work, apt-get install mono-complete is required. keepass compiles plugins and requires the whole environment in order to do this.

ensure to chmod 666 the plugin file

for the googlesync plugin, the following is required:

download sync plugin, then extract the zip from http://sourceforge.net/projects/kp-googlesync/?source=typ_redirect

sudo cp GoogleSyncPlugin.plgx /usr/lib/keepass2
sudo apt-get install liblog4net1.2-cil
sudo cp /usr/lib/cli/log4net-1.2/log4net.dll /usr/lib/keepass2
sudo cp /usr/lib/mono/2.0/System.ServiceModel.Web.dll /usr/lib/keepass2
possibly also required is the import of the mozilla root certificates:
mozroots --import --sync