I say this with the sincerest goodwill: I would recommend that you abandon any modifications to that trailer and trade it on a trailer that is properly rated to do what you want it to do.
I am not opposed to home repairs and modifications to certain items. However, when a trailer needs reinforcing, it may indicate either excessive wear, a manufacturing defect or a dangerous overload situation. In any of these instances, you may be risking your own safety and/or the safety of your fellow drivers by continuing to use the trailer or attempting to modify it.
