1. I don't think 2 brackets over 36" is enough
2. I still do not believe the side are really strong enough to support riggers without added supports
I have scottys on my lund and when I installed them on on the tracks, you could see the sides moving when you raise or lower the balls and again in rough conditionns
so I had to add the wood across the boat , which 100% solved the problem and I do believe you will find yours to be the same