What is the best solution to get trim and tab position on a nema 2000 display? What sensors have people used? The drives ssm 4's. Tabs are 380's.

any 0-5 volt position sensor and Noland box. The mercury sensor can be use outside of the boat (attached to your 380's possibly added at trim pin on ssm4)
Steve

Thanks for the reply. Are the Mercury sensors that bolt to the transom assembly accurate enough? I always thought they were not.

The new ones are good

Indy. I ended up using the livorsi units with short morse cables. The signal went into a Noland unit

I went through this exact runaround two years ago - unless you know how to create and/or modify your own PGN's, you might as well give up. The fact that the Lowrance product is obsolete with no support doesn't help. I ended up returning the Bennett kit and exchanging it for one that didn't include the "supposed" NMEA2000 capability - and then bought the Garmin GBT10. It installed fine, calibrated, and displays perfectly on the GMI10.
For a couple hundred bucks, it's not worth trying to re-engineer the Bennett/Lowrance unit. Chalk it up to one more example of N2K 'sort-of" compatibility...