Hi Jim,
I think you may find using polyester webbing instead of nylon will be a better choice for this application. Less stretch, better strength, UV resistant and won't absorb water.
The actual location of your straps looks near perfect, as they sit between two lateral supports (seat and forward thwart) .... that should fully support the gunnels at the attachment points, plus we are talking a solo canoe weight which hopefully is in the 40 pound range, so almost anything you do will most likely be over engineered for purpose.
My next project is attempting a new tarp for my Tentsile Flyte, not liking the supplied one much and feel I can do better ... that means learning to sew (a bit). The research for that is done, I have the material and am in the planning/execution phase ... I only mention this, because having an idea of what sewing can accomplish has influenced my views a bit on how to customize any projects that use material/strapping stuff.
I really like this concept and intend to a) follow this b) look at it as a option for my next solo (hopefully later this summer) ... so you asked for thoughts .....
- as above, use polyester webbing for minimum stretch
- you could adjust the shape of the V by moving the cross over point manually to form a wider/shallower V to customize to the user (lock the cross over with stitching/rivet etc.)
- wider webbing would be more comfy
- you could actually still use a stiff foam pad on the shoulder strap area .. that could be sewn in or just sliding (likely require some material covering)
- if the V angle is too severe, maybe add a gusset (silpoly or maybe wider webbing) in the crotch to better fit around the neck area
- if you get really ambitious, a set of formed pads might work really well .... I am thinking something like curved composite, with thin foam, shaped to fit and hug the users shoulder .... lock pads in place or not, depending on whether you want to be able adjust balance on the go
I love ideas like this that make you think a bit.
Brian