I made sure the deck was sanded well for painting.

Here I tapped the styrene in place so I can trace the spar deck pattern on it.

Once traced I measured the line to make two pieces. Turned out the deck is pretty flat in this area so I was able to get away with a straight cut matting to the spar deck.

Once the pieces are cut out I take one of them and tape it onto the spar deck. I used a round pin to make sure the bull work was flush with the hull edge.

Once everything looks good you can run a thin bead of thin CA to glue it in place. The tape will hold it down while you glue, yet will still come off fairly easily. Any tape stuck after removal can be easily sanded off for a good fit. Once things look good you can glue the second piece down behind the first one. So you end up with two pieces back top back, this is what gives you the strength. Then you can sand for a good fit.