He bought this homebrew landyacht secondhand and has been fixing it up for his clients to use.
It uses wheelbarrow wheels and a windsurfer sail. It carries two people in comfort and comes apart for transport.
In this video the frame twists quite a bit. After that we added two more tubes to triangulate the frame, and it doesn't twist anymore.
Step 1: The Rear Wheels
They are plenty strong and have no trouble with the side forces.
I guess they were made in America by union workers.
I built a landyacht once using cheap imported Harborfreight wheelbarrow wheels. The hubs broke off the wheels after a few minutes. You'd have to weld some braces onto those wheels to make them strong enough.
These axles are stubby things that insert into the rear aluminum tube. The axle nut has a retaining wire to keep it from spinning off.
The rusty tube seen here is one of two braces we added to triangulate the mast support. After that the frame didn't twist anymore.