Think you got two choices. If you are thin (or have a thin friend), might be able to reach up to bow via the starboard rod locker. We did it with a Puma (not at all easy), not sure about a PIII. Other option is to cut out a hole under where the trolling motor pedal is mounted in the well there. Reach under to tighten nuts. Seal hole with rubber gasket or some other material. The trolling motor will cover the ugliness of the hole. We did that with a different Puma. Watch out for glass cutting our arm when moving arm in hole! Others may have other ideas