A trailer's frame is where a great deal of its strength comes from. However, if you improve the quality and durability of the frame, your trailer will last a lot longer and be safer on the road, no matter how rough it is or how far you have to drive.
One way to increase the strength of your trailer frame is to evaluate the metal that it's made from. For instance, a lightweight, aluminium frame might be less weight to pull and easier on your pocket book, but it will bend and twist much easier than a solid steel frame. If you want strength, then you need to choose a strong, durable metal frame that isn't likely to rust or weaken over time.
Trailer frames that are welded are inherently stronger than trailers that are held together with bolts or other types of hardware. Welding creates a permanent bond between the metal and makes it as if it were a single piece that comprises the frame. However, hardware means that the joints are held together only with the strength of the components, which is far easier to break.
Selecting a proper axle can make a lot of difference in the strength of your trailer and how much stress is put on the frame. A poorly aligned axle or one that's cracked can put more stress on the frame which can lead to damage or buckling. However, a properly installed axle can balance the trailer's weight so that the frame doesn't have to support more than its share.