There was a recent mention of this Airstream in an article that highlighted the rediscovery of another such Airstream at a fish farm in Alabama. It was believed to have been destroyed in a fire in Georgia.
After the end of the Apollo moon missions and the quarantine program for returning astronauts (for which these trailers were used), the one on the Hornet was kept for the display you saw and the others were surplussed by NASA to other government agencies. All were accounted for except one that was supposed to have been sold to the Georgia Forestry Department and supposedly destroyed by a fire. However, it was recently recognized at a Federal Agriculture Department Fish Farm in Alabama where it had been used for years and then pretty much abandoned.
When reported, the authorities at the Federal level at first ignored the report since all had been accounted for. Then, one of the officials had the opportunity to check out the report and recognized the Airstream also. Much of the original quarantine equipment was still in place and the trailer was returned to the Smithsonian (?) and will be displayed as part of the Aerospace museum. I believe that is where it will be, but I can't remember for sure...my middle-aged memory isn't what it used to be and the article isn't handy at the moment.