Read an article of a lady who rode / kayaked the perimeter of the lower 48. On the road she had the Kayak in tow with most all of the gear needed for the trip. When she was on the kayak the bike and trailer was attached. Not exactly sure how she managed the water crossings, but looked like it would work.
Guess that a trailer could be defined as a tool, but this topic is going to need input for quite a few individuals. We could direct you to any # of forums here. However they will most likely have the same response.
If I were to start a DIY build (There is another forum segment...) on a Kayak trailer Most likely I would start with a kids trailer first. This gives you a base and two wheels in which to start. Material could be sourced from onlinemetals.com Or locally if you can scrap it all together. Move the trailer segment back on the kayak till you have 55-60% of the weight on the front end then make the connecting rod from the bike to the trailer. If it attaches at the seatpost or rear axle I don't think really matters. Regardless documenting the build should be an interesting read which ever forum it ends up in.
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