Thanks, all, for your kind comments on my gouache work. I am still in the trial stage, but getting more sold on it by the hour.
Dennis mentioned earlier that gouache might hide the lines in a line and wash painting so I made a little crude test on my favorite hemp paper which turned out to be the wrong kind of paper to use for line work.
I used Winsor and Newton Designer Gouache (claims to be "vibrant, opaque watercolors with a matte finish").
The top half is full strength (just damp brush) for applying over Sakura MICRON Pigma pens (archival ink). The only line that seems to have significantly obscured the ink is the white line (under the black line).
The bottom half is a light wash of gouache which seems to have an no effect on the lines at all, except somewhat for the white paint.
In the case of the Aloha Tower painting, I used pencil to draw the shapes very lightly, then went over them with Micron pens (and erased any pencil that remained). I used a light wash over everything, using "primary blue" mostly.
Maybe it's just the WHITE gouache (which I always thought of as "wite-out" for artists) is what gives gouache its reputation as very opaque. As you can see here, it is not always so. (Then again, I might be using it incorrectly).
One last thought - Dennis, what, if any, type of preservative (fixative) would I need?