rtl_tcp device index, udev and symlink

Hi guys, new member here, but been playing with rtl dongles and sdr generally for a while now. I run four rtl dongles covering 50, 70, 144 and 432MHz with websdr running on Ubuntu Mate Works quite well but I have trouble with the device indexing changing for rtl_tcp. ie sometimes a dongle gets allocated to a different band. To try and fix the issue I've given each dongle a unique serial number and created some udev rules which create symlinks for each dongle. That all works nicely. Problem is that rtl_tcp uses device indexing starting at D0 and expects D1, D2 D3 etc. whereas my symlinks are called 6mtrs, 4mtrs, 2mtrs and 70cms Not sure how to make rtl_tcp work with symlink's rather than device index. Any ideas ? Regards Tim G4WIM