I just bought the Extreme 350 from Goal Zero at a Costco roadshow to run my ARB at night and not draw down my main deep cycle/starting battery. I also like the fact that I can run the Light-a-life's and other devices from it if I need to without depending on my main battery. When I look at cost for a dual battery system, they come out pretty close (without solar panels). Obviously, a dual battery system has 3 times the capacity, but you lack portability and for me, I would have to fabricate a tray, do the wiring, additional weight of the battery, etc. Goal Zero is plug and play and no headaches.
If you have solar panels, you probably need 60 watts to be able to charge the battery as fast as you are discharging it running the fridge. With panels, I think you could sit indefinitely with cold beer on hand (assuming you have sun). I haven't purchased solar panels yet, as I do a lot of driving on most of my trips and will be charging it via 12v accessory socket. Then at night, I will have a fully charged battery to run the fridge and lights at camp.
I like the portability of the system and you can use other solar panels that are cheaper and get an adapter. It has the charge controller built into the unit so you don't have to buy a separate unit. Yes, it is pricey at first, but when you try to piece together everything they did, you will not have a package as convenient and compact as they have come up with.
For charging the Extreme 350 via the truck 12v, you need to buy a separate connector ($12).
I will be using it next week for 8 days in Death Valley and will report back.
2001 Range Rover 4.6L SE (SD rack, ladder, Warn xd9000ce, steering guard, axle guard, diff guard, sliders, coils, 33in KM2s... no chrome)
2003 4Runner 4.7L V8 (wife's)
1985 E30S52 (1985 318i w/ 1998 M3 drivetrain, OBDI and 5-lug conversion)
Far better it is to dare mighty things...even though checkered by failure, than to rank with those timid spirits who neither enjoy nor suffer much because they live in the gray twilight that knows not victory nor defeat. - theodore roosevelt