Ubuntu – Install package to use with early_command in Ubuntu preseed file

According to that documentation it looks like anywhere on the ISO you want as long as you point the path to it correctly in the preseed/url parameter. The example documentation puts it in the root of the ISO filesystem.

That being said an ISO is a not a zip file and extracting and recreating one is not as simple as a similar operation for a zip file (though there are plenty of tools that should allow you to recreate the ISO as needed). It might be simpler, if you have an http/ftp server to stick the file on briefly, to just use that for this.

To disable dhcp you need to have disable_autoconfig and not disable_dhcp:

d-i netcfg/disable_autoconfig boolean true

The netmask declartion looks also wrong. Try this instead:

d-i netcfg/get_netmask string 255.255.255.0

Check here for complete ref: B.4. Contents of the preconfiguration file (for trusty)

# If you prefer to configure the network manually, uncomment this line and
# the static network configuration below.
#d-i netcfg/disable_autoconfig boolean true

# Static network configuration.
#d-i netcfg/get_nameservers string 192.168.1.1
#d-i netcfg/get_ipaddress string 192.168.1.42
#d-i netcfg/get_netmask string 255.255.255.0
#d-i netcfg/get_gateway string 192.168.1.1
#d-i netcfg/confirm_static boolean true