FWIW, if you get a reasonable amount of trucker traffic on the standard channels on that old CB, you might put the question to them. They're probably more familiar with the gear that guys (and gals) are using. I suspect cell phones have made the SSB channels mostly dead, since cell phones now permit a private (as opposed to semi-private) conversation. And RV-ers travelling in loose groups tend toward FRS. On the other hand, dead radio bands attract off-beat users with their own interests; you never know.

EDIT: This whole conversation reminds me of the Radio Shack catalogues I drooled over as a kid. Wow.