For the 2D skimmer, I'd mount it one of 2 ways. Either the traditional rules of mounting it on the lowest vertical section between strakes/chines on the starboard side about 15 inches from the prop at a height that allows it to skim the surface of the water while running, or the better option may be shooting it though the hull in in the bilge. You can get your temp readings from the LSS-2 transducer.
For the LSS-2, the center of that step looks like the ideal place. I might check the degree of angle while the boat is sitting in the water to see how far off it may be. Maybe one of the mounts like a SternMate (www.sternmate.com
) could mount to the step and allow the angle to be adjusted. There are some pics on their site that may help. Other options are using a composite pvc board type material or star board to fabricate a wedge type mount to account for the angle.