I have sipgate trunk working with the following config
Registration String: <sipgate_number>:<sipgate_password>@sipgate.co.uk/<sipgate_number>
type=peer
host=sipgate.co.uk
insecure=very
qualify=3000
canreinvite=no
username=<sipgate_number>
fromuser=<sipgate_number>
fromdomain=
secret=<sipgate_password>
disallow=all
allow=alaw
allow=ulaw
Obviously replace <sipgate_number> and <sipgate_password> with your respective values.
This is with asterisk14 and sail-2.4.1-12, but it has been working for many previous versions.