horizontal pane inside vertical pane with tmuxinator

I want to setup a new window with tmuxinator with the panes like this:

#########
# 1 #   #
##### 3 #
# 2 #   #
#########

i.e., two main-vertical panes with the first one having an horizontal one inside of it, something along the lines of:

windows:
  - editor:
      layout: main-vertical
      panes:
        - gst
        - layout: horizontal
          - gulp
          - python script.py

Is there a simple way to achieve this without using window dimensions as in this answer ? Or some alternative to tmuxinator?

I started to use tmxup instead, here's the solution:

session_name: statuspage
windows:
- window_name: main dev
  layout: main-vertical
  shell_command_before:
    - workon statuspage
  panes:
    - shell_command:
        - python statuspage.py
    - gst
    - pwd