The bed on your utility trailer is one of the most important options you have if you are building a kit or restoring a used trailer. There are a variety of different wood and steel options that you might uses and each material has its best use.
Wood is a very easy option for most people because it is readily available. 4×8 sheets of plywood are available in a variety of thicknesses however most manufacturers suggest a 3/4 inch thickness.
Half inch thickness may also work if you have a smaller trailer and or are only expecting to haul light loads. I would not recommend it if you expect to use your trailer for hauling a ATV or large Lawn Tractor on a regular basis.
There are three types of plywood you might choose from. The standard Decking material is OSB and comes in tongue and grove edges for making tight floors in homes. Tongue and grove plywood could be a problem for some installs.
You also have standard veneer plywood that comes in a variety of grades from cabinet to C DX which is exterior grade but must be covered.
Final choice is Pressure Treated Plywood and this material is great especially if you expect to leave your trailer outside or use it in moist conditions. It has an extended life in wet conditions.
Other wood options are decking boards. Many people use standard grade building materials and although a pressure treated board might be great for weather they often come with very high moisture content from your distributor. If you could kiln dry and seal the board that would be fine but high moisture will mean lower strength. Standard Stud / construction lumber is probably your best bet.
Steel Beds for Trailers
The first thing about steel beds on trailers is that they are expensive. Even the materials if you can find them and weld them in yourself are expensive but they are a good option for people who haul landscaping equipment.
Another thing is you should realize they will require a tarp to haul any loose materials like mulch, stone or other things. This may or may not work out well for you.
And also you can get pretty heavy fines if your equipment leaks oil or if your materials cause problems for other motorists.
If you are looking for a Steel Bed I would probably suggest that you either contact your local Trailer Dealer or buy one with a steel bed already in it.
The amount of time welding and the cost of materials often makes it prohibitive for do it yourselfers.
One thing you don’t want to do is try to install fence material as a bed because it will stretch over time.