John,

 

For what it's worth, I flew my ES in 80-120 grit sanded primer for over a year before it prepped it for the paint shop.  I wiped down the whole plane, especially the belly to remove any grease.  The belly took some work, a couple passes with lacquer thinner did the job.  I gave it another coat of primer and sanded the whole plane one more time down to 320 before I took it over to the paint shop.

 

Mike Easley