I sometimes use sanding sponges around the edges and contours. Helps me get into the nooks and whatnot. On my first refin, the body I had bought, online, the edges were all out of whack from the previous owner. I ended up building them back up, with a good poly filler, and taking my time, ever so gently with sanding sponges, mostly, I got them re-contoured, properly. Looking at it, now, you'd never know.
For the front and rear faces, I usually adhere sandpaper with double-back tape, to a sheet of plate glass that I have (used to be a glass chess board), and, instead fo drawing the sandpaper across the body, using a handle mounted in the neck pocket, I draw the body across the sandpaper. Worked like a charm.
I use sandpaper and dowels for the flat faces inside the horn areas. Time consuming, but effective.