My Onan 5500 runs two 15K air units along with lights, tv and occasional microwave use. I have yet to find a time where I was limited on power. As far as noise goes, my bed is right over top of the genset and I don't find it to be any louder than the A/C unit over my bed. The one thing I was worried about was vibration, but that doesn't really seem to be an issue either.
On fifth wheel trailers, there is usually some room between the genset enclosure and the floor of the trailer. There are several ways that you can insulate to help prevent heat issues as well as use sound suppression matting to help with noise and vibration. I haven't found the need to do either, but it would be easy enough to do if you wanted it to be more quiet than it already is.