I did not want paint to drip or run through holes in the upper hull when painting got under way.
Accordingly I plugged the ventilator and portlight holes with cardboard by taping up the interior, like this.
And by then dropping a cardboard disk onto the tape, as on this ventilator hole.
That will keep out unwanted paint and debris.
I did the same to the portlight holes, as here.
Nearly ready for paint!