Hi,
I use two Costco flooded lead acid golf cart batteries in series. They are 6 volts, 220 amp-hrs, $90 each, and 60 lbs each.
The attraction for me is half the price of AGMs and they last longer.
Downsides are that the battery box has to be vented to the outside (a half hour job), and you have to add water once in a long while. My feeling on adding water once in a while is that I want to take a look at the batteries at least every six months just to make sure the terminal bolts are tight and there is not a lot of corrosion going on, and checking the water level and maybe adding a little water adds a couple minutes to the inspection -- being retired, I can afford a couple minutes every 6 months
But, the place to start on selecting batteries is to figure out what your daily loads will be and how many days you want to be able to run off batteries. This will give you the size of battery you will need.
Here is one way to do it:
http://www.buildagreenrv.com/design.../sizing-electrical-components-for-camper-van/
Depending on what your electrical loads are and how long you want to be able to run without charging, you house batteries could be anywhere from a 100 amp-hrs up to 500+ amp-hrs.
Gary