Here is a picture of BC 2's car that I took. It has two base radios in the back with a command post. The BC would also have another radio on their belt.
Anytime there are 3 or more units on a call, on of the units is required the take "command" and "field communications". Battalion Chiefs have the luxury of two radios so they can monitor both "fieldCom" (Delta for Echo or Foxtrot or Juliet for Kilo or Lima) and the fireground talkgroup. For lesser incidents, the units just have to make due. This is done for several reasons -- one - to ensure multiple units aren't calling in to fire alarm and second - because fire alarm generally only monitor the fieldcom talkgroups (particularly when they get really busy).
The VRS has been in place for years in AA County but almost never gets used. It's actually more complicated to use it than it really needs to be. In my opinion, it would be very easy for one or more units to get confused and end up totally out of radio communications when in fact it's designed to be just the opposite. It does get used for "regular' sites like Jessup prisons but that's usually done by crews assigned to the Jessup station -- it's one of those things that gets easier to use if you use it all the time... it's just not something people train on regularly so it's easy to mess it up.
In general, I believe one unit from each station has a VRS repeater including a 2nd antenna to support it - so in theory, there could always be one or more units on a incident that can serve as the "local site repeater".