I have done a good deal of testing with the snap, but I will have to report on how well it holds together longer term. ABS is typically harder, denser, and stronger than HDPE, at least based on the published values for young's modulus and density. Obviously, this does not account for behavior of a 3D print. I have not tried any HDPE snaps, but I suspect that in comparison to ABS, they would be easier to snap in due to the slipperiness, but would deform faster due to lower young's modulus.

While I do not doubt Tom's testing, I do suspect that HDPE might just be a relatively cheap, easy to machine, and readily available plastic. At least cursory searches do not yield any large sheets of ABS -- the plastic is typically injection molded rather than machined. Also, since the material is much harder, you really have to make the snaps EXACTLY the right size otherwise it just won't snap in. After a lot of experimentation, I found that at least with my printer's accuracy, a 0.7" gap for 0.75" tube yielded the best snap action. Another feature of my model is that the snap corners are rounded over, which would spread out wear over a wide circular region rather than a thin edge.

Again, I will post more once I have more extensive testing done. I am slightly worried about how much force the plastic would have to hold up when first entering into the kayak. I remain hopeful that this system will work well though :)

I should also mention that I have my own filament extruder, so I'm actually using reclaimed plastic for the prints. If it fails, it's no biggie -- the plastic was worth probably a few bucks at most! (I bought a 16 lb box of plastic for $25, and I would be surprised if this whole thing used more than 5 lbs of plastic)