[Serusers] SER & Asterisk in a non-routed environment

[Lars]

Hi serusers,

after spending 4 days trying to figure out how to set up things using 
SER I am now hoping for help.
The problem is as follows:

i have a core network (say 192.168.0.0/24) in which the asterisk 
(192.168.0.99) resides.
i have a users network (say 192.168.10.0/24) in which I (the user, 
x-lite) reside. Theres a gw between those to networks with addresses 
192.168.0.10 and 192.168.10.1.
The big problem: This gateway is not allowed to forward packets. It does 
usermode port-forwarding for required ports, but it has no default route 
and /proc/sys/net/ipv4/ip_forward is set to 0.
The asterisk is working well and i now wanted to be able to place calls 
to other users (currently one directly connected grandstream) through 
the asterisk. First i check out siproxd which almost immediately worked 
as desired, but i realized, that as soon as the 192.168.10.0 network 
will be populated with more users, i don't want the inter-user calls to 
appear on the asterisk. That's where SER comes in. I want it to sit on 
the gw-box and handle request in the users network by itself, but 
forward requests it cannot handle (e.g. pstn) to the asterisk by 
pretending to be the user himself, as siproxd does. Especially i think 
therefor a user must register at the asterisk server through SER which 
also should notice where to find him using usrloc.
I played around with nethelper/rtpproxy but could not even establish a 
sip session, not to mention rtp. I somehow don't understand the way ser 
works, and should handle meet this kind of requirement, so my question 
would be:

Is 'ser' the tool I'm looking for? And if 'yes', how would it basically 
have to be configured to do what i want. For example one problem seems 
to be, that it forwards packets to the * server from it's 192.168.10.1 
address which the * box will never know.....

Thanks a lot

Lars