Montgomery FRS TG Victor 7 Bravo

Montgomery County FRS has been using a talkgroup Victor Seven Bravo V7B to combat poor trunked coverage for river rescue operations. This is a patch of some sort. When this patch is activated, mobile units that select V7B can be heard on 7G digital and on 153.95 MHz analog but not on 7B digital.

Is this a vehicle repeater in a command officer's vehicle, which then relays back to a fixed transmitter site?
If so, how does it differ from other uses of a vehicle repeater (TG 7J)?
Why is it patched to 153.95 but not to 7B?

But the big question is, how does this solve the coverage problem?

Whatever repeater that's patched from is local to the rescue operation being performed... whether it's fixed or in a mobile setup (Battalion vehicle etc). That sorts out the coverage, that's why the patch exists.V7B might indicate V for VHF... so that might be a localized repeater for the 7B VHF patch being linked in.

Back in the 1980s, the county built additional receive sites in the Potomac River valley to enhance coverage for river rescues and other calls along the C&O canal. It operated on channel 1 (153.95 - Fireground) of their VHF system, which predates the current 800 TRS. I would imagine that some of this infrastructure is still in use for this purpose. Perhaps there is some sort of VHF crossband repeater is installed in some of the units assigned to the area? It's also possible that the USPP still have 153.95 programmed into their radios to facilitate interoperability.

It turns out that it's a cross-band patch between 7G and 153.95 MHz.
Ordinarily 153.95 is patched to 7B.
But since the 153.95 transmitters have better coverage than the 800 MHz transmitters near the river, this allows better comms with units on river incidents.
One important factor, which I did not know before, is that the 800 MHz radios also have VHF capabilities.
So when the portable radio is set to the V7B talkgroup (which isn't a talkgroup at all, but a discrete frequency), it operates on VHF but the user can access the radio system just like it was an 800 MHz TG.