If your fingers work just get them wet and it'll be way easier to separate layers of the bag.
Sawfish, an Unsinkable, Lightweight, Foam Kayak (23 Lbs). Free DIY Kayak Plans, the Hardware Store Boat
I've built a version similar to SeaFoam, the issue you are going to run into is lack of rigidity. The sawfish is relatively solid boat in comparison to Seafoam, this could be compensated for by adding bracing.
Well I kinda sorta followed your instructable. If anything it inspired me, so I reached out to Gavin and he sent me the vector files for a slightly larger 108" mouseboat. Probably going to be building a take on sawfish sooner or later.
Why not use a left hand drill bit? Seeing as the screw is in plastic it would probably just back out.
As a commercial sign manufacturer, I'm just going to say that the ampersand is literally the worst letter to build followed by cursive Q among others. If you invert your letter on blocks, you can use clamps get your return pressed tightly along the edge of the letter. This Ampersand is about 19" tall.
Shrinking the size of the drive wheel would be one way of doing it.
And here is the finished product. Thanks for reminding me about this.
Make PVC Look Like Wood