They use Channel 68 or 69 in my area.
Truckers have been heard on Ch. 71, and 19a

Looks like they are using Marine Channels according to
the FCC rules!

Not necessarily - they could be using assigned land mobile frequencies
that happen to be close enough to those marine channels that they can
be heard on a standard marine radio. As I said, you'd have to check
to see if the FCC has any land mobile allocations close to those
marine channels for use in your area.

They are using marine radios on marine channels.
A ham friend of mine has talked to them.
They are arguing that they don't need licenses,
and indeed, if the FCC does not have the money or
manpower to go after them, then this activity, like the
mess on CB will become legal by default!