A couple of recommendations.
Mount your corepack in as dry a location as physically close as possible to the drive motors.
Go up an AWG step in the power wiring
from the supply to corepack and from the corepack to the drive.
Make sure you put the chokes on the control lines.
Do you have hydraulic or mechanical steering
. I believe the the Catalinas are mechanical. Make sure the alignment from the drive motor to the steering quadrant is level.
It is not an easy install, usually because of the access to all the tight spots and finding appropriate mounting positions. But, It is not rocket science either.
Do look on Raymarine.com. They have excellant support and will be more than happy to answer questions either by phone
or via their Web support.