Update: I decided the hang the ol' Innova 3160B on the truck's OBD2 port, but it does not read long-stored ABS codes (may read and briefly display the codes as they are occurring...not sure, but worth a try). Did a ~250-mile round trip, almost all towing the camper, and no such messages appeared on the instrument cluster. Everything worked perfectly. I figured thew problem may have just resolved independently and gone away (not likely), or it had something to do with the new pair of batteries I installed two days ago (before the trip - another story altogether)... maybe being "off batteries" for an hour would cause a sufficient reset of the system, followed by a relearning of sorts (also not likely, but I'm game for most anything). I did notice an extremely brief error message on the instrument display when I started the engine after the new batteries went in... probably nothing, and it did not happen again throughout that trip.
Meanwhile, the trusty old Innova is of little or no help at this point, and I will continue to await an eventual and constant return of the problem that will show up for the dealer's "box".