Here is the trailer I purchased last January and have since modded, a Cycle Force Trail-Monster cargo trailer.
I bought this because it has a 300 pound hauling limit having complete, long welds rather than just spot welds.
The first thing I got rid of were the wheels because I didn't need 20" wheels with balloon tires that were quick release. The wheels that came with it were really junk so I replaced them with the 16" Tuff Wheels used by Bikes at Work that roll beautifully and the load is more stable being lower to the ground. I ultimately took off all of the railings and saved 10 pounds or 25% of the trailer weight and then used an under-bed storage unit that fit perfectly on the floor of the trailer and was just higher than the wheels and just used bungie straps to hold it down. This way I could use the trailer for small things or take off the lid if I hauled something higher than the top and it works well and rides quiet. Then I found the sides from a crib and used one to put on top of the under-bed storage unit and it gives me an additional 6" on the sides and a foot in length for when I need to haul bigger things.
I have no car, so my bike along with this cargo trailer is how I get around and haul everything I need to haul.