Pcmanfm doesn't use gvfs for automounting local drives, but I did some more reading, and it does look like it uses gvfs for automounting samba shares (I don't use samba so I apologize if I've given any misleading information).
Gvfs was compiled for Porteus without Samba support -- I'm looking into this now to see if I can get it to compile in. The debian 'gvfs-backends' package may or may not bring in everything from gvfs that is needed to use the samba backend, I think it will be better if we can get this compiled natively, but keep working your path as well.
Posted after 52 minutes 38 seconds:
Ok, samba support wasn't compiled in because porteus includes a stripped-down samba package, and apparently the headers (at least) were removed from the package, so the gvfs configure script couldn't find the needed libraries. I've added the full samba package on my end and recompiled gvfs, you can download the txz here:
http://porteus-xfce.googlecode.com/file ... -1Ahau.txz
This will still require gnome disk utility, here's my version (which shouldn't bring in too many deps -- I don't have time to track them all between xfce edition and kiosk edition at this point, please let me know if you need more packages):
http://porteus-xfce.googlecode.com/file ... -1Ahau.txz
Try those (remove the debian gvfs-backends package first), add any missing dependencies, and let us know if this helps...