Following up on the previous comment:
I bought a used TT with a Honda 3000 mounted on the rear bumper. With enclosure, I'm guessing around 160lbs. When I noticed the bumper rotating, I had a welding shop reinforce it similar to what has been suggested in other comments to provide support as well as stop the bumper from rotating.
At the same time, I had a 2" receiver fabricated and attached to the frame so I could carry bikes on the back. Three bikes (two of which were kids) plus the bike rack was maybe 100lbs. I have no idea re: the weight of the receiver and reinforcement, but by that time I'm guessing I was up to +/- 400lbs.
I didn't give it much thought. Until the frame bent just behind the rear axle. In fairness, it was a an ultralight trailer. It never towed poorly or gave any sign that disaster was imminent. At the end of the day, it was totaled.
In any event, especially if you have an ultralight, I'd be slow to reinforce things to carry more weight--that weight gets transferred and will show up at the next weak spot.