On my 185RB Baja, I welded a couple of metal straps to the top weld seams. That takes the tension off that weak top weld and helps keep the bottom weld in compression. I did this so that I could install a bumper-mounted receiver and use my Kuat bike carrier.
If you add anything to the bumper, I recommend following behind the trailer on typical roads to see if the movement--which can be excessive behind the axle of a trailer with no shocks--is reasonable and within the material strengths of your mounts, carriers, etc.