Not clear why you don't just replace the 33-year-old exterior antenna and especially the seals it has, and continuing to enjoy radio reception. The seals and caulking job are doubtless dried up and cracked which is why you need to keep a bucket under the opening.
That type of antenna is easily available still today, and if you take the usual care in replacing it (and use some Tempro/Vulkem to seal the hole) , I predict you will get another 30 years of good performance out of it.
In any event, to get good radio reception you must
have an external antenna, since your all-aluminum Airstream makes a wonderful Faraday cage, which effectively stops radio-frequency waves from reaching the inside of the trailer in an acceptable manner.
Plus, those external antennas look toadly cool!