I figured the single fat tire might float over the sand better than the two smaller wheels, however, mounting two fat tires on a trailer would either make for a very wide trailer (overall) or a very narrow cargo space.
The single wheel trailer seemed to be the answer.
My brother used to have a single wheeled trailer called a Bob which he took on a bike trip we made from Pittsburgh, PA to Annapolis, MD. It worked really well and was pretty stable.
Step 1: Hub for fat tire
Start by disassembling a steel front bicycle hub. Doesn't have to be anything fancy, just weldable.
I cut the hub body in half using a pipe cutter.
Next I cut a piece of 1 1/4" EMT (galvanized thin wall electrical conduit) to the proper length for the tire width, to act as a spacer for the hub halves.
- IMPORTANT - The galvanizing was ground off the ends of the EMT prior to welding)
A wheel mount disc was fabricated from a 1/4" thick steel plate, cut round, with a 1 1/4" hole drilled in the center and (4) 3/8" bolt holes drilled to match the wheel. Since the 1 1/4" EMT is an inside diameter, I had to file out the hole for a snug fit to the EMT.
Using a piece of threaded rod longer than the finished hub width, with several different sized washers, I clamped the halves of the cut hub onto the EMT spacer. With proper washer sizes, the hub self-aligned for later welding.
Before welding the hub halves to the spacer, however, the wheel mount disc must be welded to the spacer. In my case, the location was offset from center to match my wheel. I aligned the disc on the spacer it using magnetic clamps.
Then the hub halves were clamped to the ends of the spacer with the threaded rod and welded in place.