I'm in the process of re-canvasing my 15' custom built. In the past I've played with a variety of sizing techniques. 1. Clay-based filler + marine paint 2. Searing canvas with torch + polyurethane + porch paint 3. Polyurethane + Porch Paint All of these techniques have held up well, although the filler adds considerable weight. Canvas has been acceptably smooth when I scorch it but don't fill. I've been reading through recent posts trying to figure out what to do this time and seen the good suggestion of using micro-balloons as a filler. Has anyone tried adding micro-balloons directly to paint or polyurethane as a sizer? Results?