Hi Steve;

I found a neat little saw at a hobby shop, probably intended for small models. It came with 3 different blades and cost about $7 as I remember. It had the thinnest kerf of my entire small saw collection at that time, and even at that, the cut line turned out rather visible (I can't imagine what a roto-zip would produce!). It was easy to navigate around curves with the narrow tapered-to-a-point blade, more so than a wider constant width hack saw blade.

I later used a thin kerf Stanley pull saw (they call it a flush cutting saw), on my deck designs. In this case the combination of a wide (1" or so) and extremely thin & flexible blade made an easier task of following the cut line. In use, I angled the handle down and bent the blade along the curved cut lines. You can see it in use at my kayak site linked below. The pic I'm showing here is of the small hobby saw in action.

BTW, it's not necessary to drill starter holes, just begin carefully with the saw blade. The holes often have a tendency to show unless you sand them out, which widens the seam further.

Best Regards, Spidey