You need to specify port=8070 in your general section as well, unless the SBC is messing around with port numbers. The port in trunk only applies to the remote end of the association; the local end port is taken from the general section. chan_sip cannot listen on more than one port.
(Generally, the fact that you are using an SBC is of no use without specific details of how the SBC mutilates the protocol exchanges.)
There is no registration happening here as both ends are static, so your statement about registration must be false.
insecure=invite nullifies the secret setting; it is generally only useful when you are registering with the peer and are unable to control it to enable both way authentication. I don’t know why you have insecure=port. The name of this parameter should be a clue that you do not use it without good reason.
General best practice is to use type=peer. type=friend is less secure and will cause problems if a local caller ID matches a remote device name.