We are working on staging our home for sale. Part of that is replacing the "hollywood" bar lights over the mirrors in both bathrooms. In case you're wondering, they looked somewhat like this:

DIY Vanity Light Installation - a set on Flickr

After I bought the new lights, I realized that there wasn't an electrical box. My search on the internet confirms this, but I can't find how to install one. The boxes I seem to be able to find are for ceiling fixtures. I'm pretty sure I don't need to use a pancake box like the guy in the above link. But I did see that he braced the box to the nearby studs. Do I need to do this as well? Once I have the box in, I think I'll be OK. I replaced 6 ceiling lights in the house already. :)

Oh, and the house is newly painted, with holes already textured, so I'm trying to avoid making new holes as much as possible.

Thanks for your help in advance!