We had an old Dash-8 that took aprroximately 2.0 degrees of LEFT aileron trim and 2.5 of RIGHT rudder to stay wings-level in cruise; stayed in almost the same configuration through cruise and descent (give or take a little rudder with power changes) until bringing the props up to max RPM during the landing checklist, whereupon the plane asked you very firmly to neutralize it's aileron trim. No spoiler problems, trim indication was fine. Best we could figure it was just bent to snot, but it passed all the airframe tests they could put it through. Never did figure that one out.