Some of those "kits" are hideously expensive. And if that GoalZero doesn't have a convenient way to replace the battery (check the manual) do NOT buy it. Batteries don't last forever, and if you have to replace the whole kit when that happens you've been ripped off. The price of that is approaching the price of Lithium ion or lipo batteries, which charge much more quickly.
Best is to go to an RV place and just have it built in. It's not super difficult, but there are a bunch of considerations. You need to isolate the house and engine electrical, prevent against shorts and fires, etc.
Otherwise, I agree with others that what you need is a battery box, a deep cycle battery (tons online or at RV or boating places), an AC charger for it to plug into a wall socket, a DC charger to plug into your van, and a small inverter. The latter is available at Harbor Freight for cheap. And a few cables.
Here's a 12v kit that isn't too different from one I've used:
http://www.powerstream.com/BP-60.htm
They also make a good charger you'd want for a vehicle:
http://www.powerstream.com/pst-pb1108.htm
The thing is as power needs increase so does the need for recharge, and then it becomes much more convenient to have a built-in system.