This might be a dumb question? But you specified the Trailer is 1999... I assume you are using a brand new HD Digital TV? As standard broadcast no longer occurs in many areas... Therefore: if you are using an older TV that does not have a digital tuner you wont get much if anything...
As I used to sell antennas for Radio Shack in the 90's "Digital ready" antenna is a crock... As Digital signal can be received by just about any Television antenna..
The only other thing to possibly check... As the Trailer is "Close" to 20 years old you may want to check/replace the connection on the cable up on the roof..
Hope that helps.
Cheers!
MrJoelieC