Thinking more about this. Although a base mobile/base version most likely isn't in the cards, a mobile cradle for a G4/G5 might be an option. The G4/G5 would sit in the cradle, with connections for an external antenna, power and external speaker. Similar to an amplified base, but without the speaker and amp.
I'm planning on buying an amplified base after I get my G4, but it would be hard to mount the amplified base in my SUV. There's just not enough real estate for something like that and I don't want it tumbling around the passenger seat.
At least dreams are still free.....