If you want to use full features of pcmanfm, such as auto-mount handling on
removable devices and trash support, just follow these instuctions below:

1) install these two additional packages (and obviously their dependencies):
  -gvfs
  -gnome-mount

2) In your .xinitrc file (or your window manager's startup file), edit the
'exec' line like the following (<WM> stands for your Window Manager command
(e.g. lxsession, startfluxbox, etc):

  exec dbus-launch ck-launch-session <WM>

3) Restart your WM and try.