The angularity of the engine mounted in the boat will influence how the oil sits in the pan (at rest). If the engine has a steep angle, the oil will level itself higher on one side and possibly be over the tray. With that being said, the angle of the boat on the trailer or in the water (at rest) may compound that problem.
Once you get it worked out, run the engine to bleed the system and trim the dipstick tube to indicate where you want it.