Like Groswald, I also have a Porter Cable 150PSI Air Compressor that I bolted into my rear storage compartment. It is powered by 120VAC, but all I need to do if I have an emergency on the road is to start the generator. But if I just need to routinely fill air, if at home or at a RV park, then AC power will be available.
My compressor takes about 3 minutes to initially fill the tank, but then they can fill a 80psi tire fast enough in my opinion. If you are filling 100PSI tires, then that may take awhile.
Porter Cable makes several different pancakes, and the 135PSI or smaller compressors make take more time to fill tires, but the 150PSI/6 gallon tank model to me is adequate.
As well, in my view, the 12VDC compressors just take too long to fill tires.
I paid around $100 for the compressor when they were on sale at Amazon. I have an older model, and the current 150PSI model looks a bit different.
I have found many uses for the compressor as it is attached to the RV, including filling tires (both RV and bicycle), winterizing the water lines, blowing dirt out of things, and blowing up water toys. In fact, when at the RV park, when other campers hear my compressor start up, I often get a couple of "customers" needing their bicycle tires or beach balls inflated.
When you are blowing out water lines, you want a compressor that has an adjustable regulator (the Porter Cable does). That way, you can turn the pressure down to blow out the water lines. I typically use around 5PSI to blow the lines, which is adequate.
You could probably use up to 30PSI or so as water pressure is often higher than that, but I have found you can use far lower air pressure to blow the lines. That way, you don't risk damaging your plumbing.
If the air compressor does not have a regulator, you have no control over how much air pressure is used. So I would highly recommend an adjustable pressure regulator for any compressor used to blow the water lines.
To bolt in the compressor, I simply put longer bolts through the mounting feet to attach it to the base of the storage compartment.
One thing I had to change though is to go to a quarter-turn air relief valve, as my particular model's stock valve was hard to use when the compressor was bolted down.