What type of boat are you mounting to? Good idea to use a backing plate on the underside to distribute stress. Do not use screws, bolt through, use S/S.
There is an incredible amount of stress on the swivel, mounting pedestal and Gunwhale or whatever your mounting to. Have also heard of bracket or swivel failures.
It is good idea to tether the downrigger with strap or aircraft cable to an independent eye bolt.
The power cable may save you, but who would want to count on that to save your $500+ investment.
On my 16 alum. there was some sideways flex so I added a gusset brace.