For starters I'll get the SSB power off the main circuit panel, re-route the cable from the SSB to the tuner, and add a Ferrite Line isolater between the Radio and the tuner.
The compass sensor is already mounted low in the hull, the CPU is well away from the backstay, and I do have flat copper from the tuner to the keel, so am all set in those areas. If I still have problems I'll start digging deeper. I might look into the KISS ground system; it requires no connections, perhaps that would help isolate it from the rest of the equipment.

Thanks again for the suggestions.

Max