I had to do some grinding on mine to get the nut to sit flat. If you don't want to grind then another option would be to just glue it in place with 3M 5200.
Mounted in this location there is there a way to "run a loop" to keep water from running in when the skis upside down?
Just leave the pump running while your riding it won't hurt it a lot of the salt water guys hard wire them to the battery and disconnect them when they are done riding