RV Repair: RV Battery Discharge, dutchman tent trailer, deep cycle battery

Question
Hi,
Just purchased a 1997 Dutchman tent trailer from a private party. I installed a new deep cycle battery, which completely discharged in one hour after running the heater.  I don't know much about the wiring and operation.  However, I assume the battery should last longer than this.  The samething happened with another battery.  What could be the problem?  Everything works fine when connected to 120, except that I have to turn the thermostat off to shut down the heater. Shouldn't the battery charge when our vehicle is running?  How long should a battery last while running the heater and one overhead light?  Also, since I do not have an owners manual, can you tell me what the dial knob(numbered 0 - 7)is for on the control panel?  I suspect it is a temp setting for the refrigerator.  Lastly, it appears that something (box shaped) has been removed from under the bench seat, directly behing the power converter and next to the water tank.  Several screws were left in the floor, where this unit was attached.  Looks like it was about 10-in. square.  Thank you for your response.

Answer
Hi Rick
You better check that refrigerator, I'll wager its turn onto 12 volt dc and that is the problem. No way a fun. would kill a new batty in an hour.
The batty should charge with the vehicle in tow, but only if the wiring was done or done right. The mystery box may have been a 2nd battery.

Thom