I also used a 12" Stanley SurForm with a convex bottom. I then used a 1/4 sheet finish sander by cutting a 1" thick piece of styrofaom the size of the sanding pad, rounding of the coerners by the paper clamps with a fine saw and cutting the paper 1/8" along. By streching the paper tight on the styrofaom the foam stayed in place (a piece of two-sided tape would help). The styrofaom also tends to slowly sand down with use and will fit the curves perfectly. The short pieces of sand paper still fit the sander without the styrofoam for flat work or the outside of the canoe. I also used the 12" SurForm but with a flat bottom on the outside of the canoe.