I put dead man walking, threes a company and by the book all back to back to focus on that story arc. Michael has also been away from home a lot during that time. Then I'll do scouting the port after by the book because at the warehouse where you torture mr k you can see the port of Los santos in the background. So I imagine that on the way to the warehouse trevor saw the port and maybe thought it was worth scouting for something to steal. So after dropping mr k at the airport he goes back to the port to investigate but realises only dockworkers are permitted to enter. Then he hears that floyd works at the docks and decides to pose as a dock worker to scout the place. it dosen't really make sense if you do scouting the port before by the book because how would trevor know about the port?. You could of course go around that area in free roam but I think it's better for story reasons for trevor to do by the book first, see the port in the background of the warehouse then decide to go scouting.