ive worked on composite aircraft, and its standard in my case to see i ground bus some where under the inst panel, with a dirty big wire going to the battery negative.
make sure you only ground your shields at 1 end, (are you useing twisted pairs, if so that will also help). also see if you can bond the rack too ground.
also make sure you intercom/ audio wiring is shielded,
would also look into static discharge... dont know if it would be a problem, but some things i imagine would build up static? and i wouldnt no how to stop it on a wood A/C