Well I wish I would have though of this a lot sooner. But anywhere it says to remove the powder coat, don't waste your time sanding. It can take hours in the case of the rudder torque tubes. Instead go to your hardware store and buy permatex gasket remover. Tape off the area you want to remove the poweder coat, spray on the remover, and hit it with a wire brush. Finish up with a wipe of the rags. It takes seconds. For removing the powder coat from the inside of a tube I found using a plumbing brush for copper pipe to work well.