Sorry for my late answer, somehow I've destroid my current AS ABAP installation (DB corruption) so I have to revert to my backup.
Thank you for your answers though. Will try to install a test certificate to try the SSL solution. Will report back next week. But this cannot be the final solution, because it should be possible to connect to NW Gateway without SSL IMO.
P.S.: Steffen Froehlich : nice badge below your name. I still have to get used of it ;-)