The Titanic build requires a modification to the vertical plates add-on, so consider this a CQD message from the Blockland Titanic team.
Here is a one-image summary of our problem here:

The blue is where we anticipate that a wall will be located, while the vertical plates are where they will end up unless a change is made. Notice how the white ghost brick is outside of the line. Making the walls 2 units thick will make the rooms significantly more cramped, so we need a set of vertical plates which can be placed back-to-back within the width of a single stud so that both sides able to be painted (or at least planted in) different colors.