I know it doesn't look pretty, but that is part of the point. It doesn't need to be because it is the underneath.

I wouldn't have even bothered to bevel the side rails with a belt sander, but I needed to make the hollow in the seat a bit wider. I had misjudged the width.

The technique could probably do with a bit of fine tuning, but it works pretty well.

Part of the appeal is that subtle changes can be made to how the seat supports various parts of your nether regions and no-one would ever see the extra bit glued on or ground off. Much neater (on the top) than attacking the top surface with an angle grinder, and certainly better if support needed to be added rather than removed.

When I sit in it, it feels like a traditional mincell seat and for several minutes after I get out of the kayak, it even looks like one, with no blemishes in the surface.