dadiOH wrote:

Which is why we need some decent "sanding surfacer" paints. Such are
common in autobody paints and relatively common in marine paints.

Best I ever found was an InterLux paint that had been formulated
especially for surfacing woods such as luan. Very heavy bodied, dried
fast and sanded like a dream...you could make a baby's ass out of
anything. Unfortunately it was very expensive. Even more
unfortunately, it doesn't seem to be available any more.

I think you're talking about Interlux's Pre-Kote. Great stuff. In
general, any marine product is going to be far superior to residential
paints.
http://www.boatersland.com/prekote.html
Pre-Kote has microspheres (I know them as microballons, but same thing)
which are a staple of the fiberglass industry. As you said, the stuff
is pricey, but if you value your time above $20/hour, it makes sense.

The paint is out there.

R