Been a while since I used it last, but here's the config I used. I've removed all other comments. The last line is the IP on your local network of the XEP. In this case, when I telnet to port 2601 on my local PC, which is running STunnel, it then opens an SSL connection to the XEP, also on 2601. At that point, you're speaking the M1's RS232 protocol.
As previously noted, this is good for events, status, etc., but not for programming ala RP.
Note that you don't need a cert, because this is only one way SSL. That is, you're only "trusting" the XEP's cert to establish an encrypted connection, the XEP is not checking for a client cert for authentication.
; Certificate/key is needed in server mode and optional in client mode
; The default certificate is provided only for testing and should not
; be used in a production environment
cert = stunnel.pem
;key = stunnel.pem
; Some performance tunings
socket = l:TCP_NODELAY=1
socket = r:TCP_NODELAY=1
; Some debugging stuff useful for troubleshooting
debug = 7
output = stunnel.log
; Use it for client mode
client = yes
; Service-level configuration
accept = 2601
connect = 192.168.0.251:2601