Not exactly what you are asking; I made "receiver style" mounts for bicycle racks, Two receiver tubes each side of the trailer ahead of the axle to accept tubes that support bike racks that were originally intended for roof rack mounting.

The receivers are square steel tube, about 1/8" wall and are bolted through the trailer floor with large washers inside. Trailer sides not used for support at all. The floor mount is solid, secure, and easily supports the bicycle with rider sitting on it (only tested while stationary .