Upol do a spray, intended as a texture paint for repairing plastic bumpers. It comes in several grades and I have found the finest to give the best affect on the Tamar.
The grip paint on a Tamar looks sprayed I think so is very subtle as you say.
Note the roof. Just a flatter finish than on the smooth parts would probably look good. That's what I shall try.
In earlier times, the grip paint was applied to decks with a big brush and was very uneven in places. I did one like it once and it looked awful, like I could do no better.