Painting the topsides this year. I have a real issue with sanding out the Interlux Precoat primer. Got it all sanded down nice with 320 grit in the shimmy sander (didn't have 320 disks for the RO sander). Took a hose to it to wash it down, and noticed I still had brush streaks that the sander hadn't removed. Wet sanding with a block works fine, but is a LOT of work and tough on the wrist. So I guess my question is whether anyone has found a way around the soft foam cushion pads in the sanders? I've made up a 4x4 piece of formica to put under the paper, but I fully expect the sander to toss it out the side. I'd really like to get the primer flat at 320 grit before putting on color.