Bench grinder
I have a 1/2 hp cheapie from Sears that runs my Scotch Brite wheel. I have used a yellow Harbor Freight grinder that was way underpowered - don't get one of those. On the shaft end opposite the Scotch Brite wheel I have a polishing pad that has been real handy for keeping the flush riveting set shiny and polished. The flush sets tend to accumulate smears of aluminum which can mar the skin around future rivets. (You can also use masking tape on the flush set..a better idea, actually. Nonetheless, the polishing pad has been useful.)
As far as my bench grinder goes, I almost never use it (7 inch Dayton, two wheels) to build an RV. Much more useful are the 12 inch disk sander and the 1 inch belt sander. The Delta (imported, of course) 1 inch belt sander also has an integral 6 inch disc sander. That one tool would probably be enough for an RV project, but the power of the 12 incher is nice. Works well on aluminum and steel.
(Yes, I know that some people say you shouldn't mix Al and steel on the same tool, corrosion or Thermite production or some such. I'll take my chances on that one. My machine shop contact thought that the Thermite story (aluminum and steel powder mixing) was pretty far fetched, but according to the internet (!), FWIW, someone has had a brief but memorable flash fire they attributed to homemade Thermite.)
I also impulsively bought another real cheapie Sears bench grinder (on sale, includes useless speed control) to use with a wire wheel. Handy for removing rust from steel. It is low on power but OK for light use.