Although most of the general public doesn't know it yet, there is a huge need for bicycle trailers. With trailers, bicycles gain a major leap in their climb to accepted transportation.
Many people stick with engine-powered vehicles because of their cargo carrying capability.
Trailers behind bicycles can pull several cubic feet, and up to seven hundred pounds on fairly level ground. The only remaining problem is that there are few suppliers of industrial-quality bike trailers. Perhaps you can fill that need. You will have to have welding and cutting equipment, and a good design or two. Make and show some prototypes, and the rest of the selling job ought to be easy.