Dear Gyp - the new Airstreams with the Flying Cloud trim line have the inside aluminum walls covered with what is commonly referred to as "mouse fur". It's a non-woven carpet like stuff - a bit like felt - a bit like the scotch brite scrubbing pads but not abrasive. The stuff really cuts down on echo.
BTW, I'm pretty sure Colin will tell you the biggest problem with fixing the floor is getting it cut to the right size with the correct curves - These trailers are put together one at a time and the old ones especially are not identical. One thread I read years ago had an owner who had really bad rot on one corner - so the enterprising owner simply found the midline, made a pattern of the good side and flipped it to get the correct curve for the missing corner... then the shell wouldn't fit back on. LUCKILY? the body on the affected corner was a bit smaller than the floor, so the man had to shave down the corner a bit at a time to get it to fit. He'd never noticed that the unit was asymetrical.
Today is a gift, that's why they call it the present.