That was my first and only attempt at music on wheels. As long as you're not expecting anything real powerful, that kind of setup should work fine.
I have not used the amp you linked to, but it looks good to me.
I used a 12 volt battery similar to this one:
http://www.sears.com/shc/s/p_10153_1260 ... 3274063580
It's a rechargeable battery, so you would need a charger of some kind in order to keep using it after the burn. While it's not huge (around 6"x4"x3"), it's still got some pretty hefty weight to it. There are other many other sizes to choose from, so you can get whatever suits your needs, like one large capacity battery that lasts a long time, or two or three smaller capacity batteries that you can swap out.
Connecting a battery like this is when things start to get a little tricky. You want to make sure the amp has a DC-in plug. (DC is the current that batteries run on. I see the amp you referenced has a DC-in plug on the back.) Then you take the wall outlet plug that is included with the unit, cut off the wall plug end, then strip off about 1" of the plastic sleeve off the wires. Then you plug the connector end into your amp as normal, and connect the bare wires at the other end directly to the terminals on the battery. That is the real tricky part, because if you cross the wires (that is, connect the wrong wire to the wrong battery terminal) you will fry the amp. (Meaning, totally kill it. I have done that before.)
In my case, I found an old wall plug unit that fit, so I didn't have to cut the one that came with my amp. You might also be able to find a simple cord with the right size connector and bare wires at an electronics store.