Holes in the frame are generally frowned upon since, depending on the location and size of the hole, it can create a weak point and concentrate stresses. Any specific information about the effect of location and size would require an engineer to figure out for you.
I never heard of a sway control ball that mounts on the trailer frame. I had a Reese friction unit for a while, but the little ball mounts on the hitch at the back of the tow vehicle, not on the trailer frame. Whay kind do you have?
Bill
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