Trunk gutter sanding

I used a gunk remover to get the part of the weather stripping adhesive that was stuck in the channel. I have seen people use a wire brush on a drill or different type things. I just used an 80 grit sandpaper and did mine by hand. I followed the 80 frit with a 220 to smooth it out before shooting my primer. Such a small area, wasn't to bad to do by hand. Good luck