slip start on boot

Hi,
The command below runs OK in terminal but I need to run on boot. - I have no experience of systemd and init.d scripts, but think one or the other is what I need to use.

slattach -L -p slip -s 9600 /dev/ttyAMA0&

After that I need to set up my network interface - will manually editing /etc/network/interfaces work?
Hope someone can help :question:

Pop it into /etc/rc.local, above exit 0, this is the last item to launch during boot.

After that I need to set up my network interface - will manually editing /etc/network/interfaces work?

Yep, but after making changes, you’ll need to restart the network interface, eg:

systemctl daemon-reload
ifdown eth0
ifup eth0

Hi,
I cannot get my routing to persist over reboot, I think it must be something to do with using an ‘unusual’ interface, as It works fine for eth0 (on a different device) can you suggest a work-around ?
/etc/network/interfaces.

### SLIP interface ###
allow-hotplug sl0
iface sl0 inet static
address 10.214.255.1
netmask 255.255.255.254
gateway 10.214.254.101
post-up route add -host 10.214.254.190 gw 10.214.255.1 sl0

BTW the excellent support on this forum is very much appreciated