Originally Posted by treilley
Forget the dedicated sanders. Buy a Fein multi master and now you have a tool that will work well for this job plus many others.
I second the multi-tool. I bought one for general sanding and it's perfect for getting into tight spaces on boats and is probably he best sander for doing a narrow rail. On top of that you can slap on a whole variety of blades and scrapers. Fein is very expensive but high quality, other versions are $100 or less. If I were buying a plug-in I'd look at dremel's version first.
Personally I have milwaukee's M12 version along with the M12 Dremel and M12 right angle drill. I'm a fan of Milwaukee for having all these tools in one line sharing batteries. I believe the multi-tool comes with two batteries which will let you run continuously if you need too.