It seems to me at first thought it would be difficult to make it go... The primary problem would be (as always) location. If people have to drive any distance to get to the shop, it would increase the time to build (thus cost to the client), and decrease inthusiasim for the service.

Personally I do not would not need the service, as I have a place to build that is far to convienent (basement). In my zelot type mission to get friends to build a kayak, I'm usually pressing folks to try it out. Those that are some what interested, often say no, as they have 'no place to build it'. Which suggests you may have a market audience.

I think it would help if you were setup near a kayak/canoe kit selling place, perhaps you could setup some kind of agreement for use of you shop and tools with them. They could draw in the odd customer for you that wanders into their shop, and vice versa.

In my case, I'm considering running a volunteer type course to build kayaks/canoes. For this your setup would be ideal (assuming I could find students). The course would be run in conjunction with a local paddleing group, so Likely I could, but I think it would be a 'once or twice' type event.
But would give a possible alternate location.

Perhaps close to a school that teaches wood working and the like?

A final thought, is what if you had the ability to 'move shop' that is your primary investment would be tools. If you could run short term leases, you could advertise courses, or events for areas, and then find space near by to make it go.

I seem to recall the cost for a building course is a few hundered dollars (above materials). So if you could have a 'expert' on hand to help out, that would help justify the added cost to rent building space. If that expert is you, all the better.

Sounds interesting to me...

Well thouse are some random thoughts off the top of my head, good luck if you go for it.

Myrl