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.
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland
Bob