I'm mounting SMBFS shares fine through scripts, so can you give an example of your script that doesn't work?
FYI, you actually don't need Samba installed for using SMBFS.
As for stopping a share, RTFM. Write Status in CLI to see which process you have to break, and then write Break to break the connection.
My script is very easy, changed today to the following line:
RUN SMBFS Volume="name volume" Workgroup=WORKGROUP Service=//computer/directory
I also changed stack to 32768...
Most of the times it hangs and only some it works...

First I had also >nil: but without it I can CTLR+C to stop!

If I copy the line to a CLI line everything works always (apart my CTRL+C problem... if I close this way the PC hangs...).
Since I am not so good in AmigaOS:
° I created the file with editpad and saved it;
° I opened the info for the file;
° I have the "V" (I do not know the word in English!) for script and removed the one for executable;
° I changed the stack today to 32768;
° Priority 0???
° Have I to executo from Workbench? Now I have this doubt... is it better to run from CLI?
° I change the association from editpad to iconx...
anf, anf, anf...
Where am I wrong?