My 2cents...
FSW WW has the Onan5500 under bed.
Its in a insulated sheet metal box. Not real thick insulation. Have thought about adding some 1" duct board to its sides where its under the bed.But not so sure it would even help, since a lot of the noise probably is coming from outside thru the genny cover/door/exhaust and the sound is 'leaking in the window right above it...
Its not loud, and just a very little vibration. But you most definitely can hear, feel it running. For an afternoon nap, not a problem at all, barely know its running. But at night when its very quite, well sure some would not be bothered, but I can't go to sleep at nite with genny running under my bed. Maybe for a combination of reasons. Probably not a great idea to leave a genny running all nite for multiple reasons. But in PHX summer heat or similar, it might be a necessity and then much easier to accept its slight noise/vibs.
jmo
When you go to look at the TH, might want to start up the genny and lay in the bed and see for yourself..?