I've never had that problem using microballoons in the epoxy. I also use a
hard back disk in my (makita) DA sander or a long sanding block. I use it to
fill (chink) the gaps in the old cedar strips. More of a problem (than epoxy)
is the clinch nails not sanding flush.
Greg Sefton

Glenn. I definitely was not trying to save a few dollars on epoxy. I use
epoxy all the time -the sanding issue is my concern, a point picked up by
others. I want the boat to be finished to show the natural grain of the
wood, and ordinarily this is OK with epoxy except that I have had problems
in the past with sanding an epoxy/softwood join, even using microballoons.
I have sometimes found it difficult to get a nicely flared joint without
sanding down the wood too far. I must admit though that I like your long
sanding boards. This may do the trick.