I'd also be concerned about the glue you might use:
a) sticking to the (assumed) existing wallcovering or
b) sticking to the bare aluminum
c) "hanging in there" with the high temps our trailers are subjected to when stored or locked up
I know I've seen a lot of factory installed vinyl wallcovering that is failing over time - and that's been bonded to the aluminum panels prior to being made into an Airstream.
Also, how would the grasscloth adhere to the rivets? The "walls" are not flat & smooth, so you would have air pockets at each rivet.