Multiple charging devices should not be a problem if they all are set for your battery type. Installing behind the breaker box suggests they used existing wiring which could be a concern. The ventilation issue makes me wonder what else they did?
Maybe there is some simple Xantrex issue. It's also possible that you now have a battery issue so have them tested. The charger should supply all house amps up to it's limit and hold the voltage at about 13.6V.
I would check and record both the amps and voltage during a charge cycle along with all model numbers etc and seek help.
Well stated 2oldman.