I've had good results with a brush. I put down a light base color, then drip out four or five different slightly darker colors on a palette. With a fine tipped brush, I use a little length of 1/4" x 1/4" wood about 2" long as a brush rest, and lay down a short little stroke. I find that about 1" looks right at 1/350 scale, probably 20 some feet long.
Do a pattern in one color, let it drt a little, which with acrylics is in minutes, then go back with each color. It's not really neccesary to have them touch, because all you are doing is tricking the eye to think that there's a variation.A real deck is actually a pretty monotonous color unless it's wet, so go easy.
BTW I much prefer this technique to real wood overlays.