Wow, do not know the standard practices for a wooden airframe and grounding. Does it even have or need static wicks (not much of a GA guy).
It would not be a bad idea to shield any wire that carries a signal, also do your best to seperate wires that carry current from those that are signal carriers.
I suppose grounding shields to the rack would be a good idea but what is the rack grounded to?
On the aircraft I am familiar with grnd is a big conductive alluminum tube and wings with static dischargers that play a big part in keeping radio transmissions clear.
Ok, for wooden airframes all grounds are wired to the engine. I would ground to the tray and have a decent bonding strap going from the tray to the engine.