If you are looking for a single compressor to do double duty (your RV and your shop) you might want to look into this (it is what I use) if you aren't a boondocker that has to have 12v. Even if you are, most hardcore boondockers carry a generator...
Aluminum 4.6 gallon CompressorIt fits into the forward storage bay and is plugged into the 120v system of the trailer. It is light, compact and has twin 2.3 gallon storage tanks for 4.6 total gallons of "stored" air under pressure. When at a campground, with two of the coiled air hoses, I can reach all of the tires on the trailer and the truck without removing it. When on the road, the almost 5 gallons of air is more than ample to air up a slow leaker to get to someplace to make a repair. It is also so light that it is easily carried to your shop or garage. I have 5 other compressors spread around my property, but, none of them are near as quiet as this one and it is hardly noticed when I use it at a campground. Quite capable of running air tools or sprayers. If one of my other compressors dies, it will be replaced by another of these.
There are lots of options out there and I'm not real sure what your "out of RV" use for it would be, but, one of the drawbacks to most 12v units is the lack of a tank and you almost have to have a tank to run air tools or paintsprayers.