I am building one myself. Slowly, surely moving forward. Eventually I will post the system here for the experts to see.
You need to answer a couple of questions before you can decide what works for you: How much power do you need? How long do you need that power to be available? How are you going to recharge the system? And since you want portable: how are you going to transport it? (Mine won't fit in my car, but will fit in my wife's vehicle).