In our 41 Sharki, we had 3/8" tongue/groove ash milled for us. We
directly covered the vinyl and screwed into the ceiling with no
problems. We did main cabin first 2 years ago and no problems. We
did V-berth this past December. We did ourselves with a little
instruction from a woodworking friend. It looks great! Now on to
the back berth! Then we will tackle the "halls".