Have missed two days when I could do the big bottom layup, it is just too cold in the shed. This may have been a factor in the crappy NACA layup result.
Bought some insulating foam and plugged all the obvious holes. Shed went from 8C to 10C while I was doing it, so will attempt again Saturday. (Work interfering before then). An hour after I turned the heater off it was still 9C, and had plummeted to 3C outside.
Insulating foam was jolly interesting, marked as Polyfoam, really stiff & light. Not intending to use it for anything, but may be good for forms & stuff, coz I have some spare. Will put some epoxy on it and see what happens.