Setting default theme for Plank on Ubuntu 20.04 using Cubic

I am trying to create a custom distro based on Ubuntu using Cubic. I have installed Plank and it works fine when using the Try Distro screen when booting into the vm that Cubic provides. I have copied over some plank theme files into the right directory but I don't know how to set the default theme for plank from the terminal.

I have tried the following:

gsettings set net.launchpad.plank.dock.settings:/net/launchpad/plank/docks/dock1/ theme 'myiostheme'

When I do a gsettings get, it shows the theme has changed, but when booting from the live-usb it shows the default Plank theme.

I would appreciate any help I can get

Gsetting works at runtime. But you need permanent setting. You can apply it using dconf as follows on Cubic image creation:

sudo mkdir -p /etc/dconf/profile

cat <<EOF | sudo tee /etc/dconf/profile/user
user-db:user
system-db:local
EOF

sudo mkdir -p /etc/dconf/db/local.d

cat <<EOF | sudo tee /etc/dconf/db/local.d/00-cubic
[net/launchpad/plank/docks/dock1]
theme='Matte'
EOF

sudo dconf update

Other possible way is to create desktop-autostart file for all users and place it into /etc/xdg/autostart as follows:

cat <<EOF | sudo tee /etc/xdg/autostart/plank-theme.desktop
[Desktop Entry]
Name=Set Plank Theme
Comment=Set Plank Theme
Exec="gsettings set net.launchpad.plank.dock.settings:/net/launchpad/plank/docks/dock1/ theme 'myiostheme'"
Terminal=false
NoDisplay=true
Type=Application
EOF

and it will executed on login.