I wish I had a single-wheel trailer, but I do have one with two wheels. It is supposedly rated for 100lbs, but may hold more now. Today's project involved riveting aluminum C-channel pieced to support the nylon bottom.
If it's a Burley, 3/8 alum bar stock will slide right in the brackets. The plywood deck can then sit or be screwed to the bar stock.
If you're packing an Elk out on rough terrain, a single wheel bob trailer sucks big time. Two wheels will keep the trailer upright.