The xantrex inverters, although full of great sounding features, do not have a very good reputation among many folks that deal with renewable energy for a living. The Trojan batteries are also a thing of the past (many years ago they were the battery of choice, but have since gone by the wayside). The other bad thing about buying used batteries is that it's really hard to tell what kind of shape they are in or how they were used throughout their lifespan thus far. Batteries can last anywhere from 2-20 years depending on how they were treated. The more times that you drain them to lower levels the shorter their expected lifespan. For example, if you use up only 5% of your battery bank capacity every day, your batteries may last 20 years, but if you use 80% of your capacity every day then they might only last 2 years. Other factors like how often they have been equalized and if they have been equalized correctly also play an important role in battery life.
I found a great deal through a small company in southern CA. Look them up or give them a call (800) 341 7027 or google Hardy Solar. The lady that does the engineering for the company wires up everything for ya and sends it to you ready to hang on the wall and do the final simple connections. I was quoted a price pretty similar to what is being asked for that trailer and that is for all new equipment and everything needed to set up the system. YMMV