It has a plate that will distribute the force of the bolt. It's pretty big. You can see it in the pic if you look close. Look at my fingers holding it.
When I ran that enclosed box at Daytona, it was being held in place with only 3 bolts with washers. I did use some rubber washers to help absorb the shock but considering the flex that whole box saw, I'm sure you'll be fine. Actually, since your system is mounted almost upside down, your system will see less stress than mine did because the system is being held almost completely in tension. I bet you don't even need the plate but it won't hurt. Maybe even squeeze some turf in between the polycarbonate and the hull and between the polycarbonate and the metal plate you made.