My Argosy had a sidemount car type antenna as you describe and
the crank-up roof TV antenna. I think car type antenna had something to do with radio, though haven't tested it out. FM reception inside the trailer is just fine. Do I guess AM? I recall that the shell interferes with some frequency and it's obviously not FM. I really wonder if converting that one would give you very much for TV reception.
The crank-up roof TV antennas were a miniature version of a housetop antenna. I'd suggest doing a search on keywords: antenna, batwing. See what you find -- I know this has been dealt with in some detail.
The batwing search just might start you early on some Halloween recipes...