Well at least you have four screws.
Is your bracket T shaped. The Springdales are!
Mine is L shaped with 3 screws. I have to tighten one side up every other trip.
My buddy has an older Cougar with the same problem. The doors are too big. So we are deciding to weld the supports on a 3" x 6" steel, then paint it and screw it with 6-8 screw giving it a bigger footprint.
I measured one side too the other and they are not even, on each side on the door and side, somebody does not now how to use a tape measure. I hope this fixes my problem. Know wonder why my door looks a little higher on one side than the other.
Read my post on your outdoor sink.
Actually its not that bad after you think about it, but it would of been nice to know.