I have had a half-built hollow wooden mini simmons in my basement. I have no time for tinkering. The final product was much better than I thought after watching the process. Not a bad approach but will still end up spending a few hundo and a lot of time.
Only flaw I see is that it's lacking is a 4x4 Douglas fir stringer. Pressure treated of course. Other than that, the dude now needs to build a paddle. You could probably get at least 6 out of a 3/4" sheet of ply wood. Pressure treated of course.