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If a 110AH battery goes flat in two hours, an incredibly short time, it must be theoretically discharging at 55Amps. At 12 V, this equates to 55 x 12 =660W. This is over half a kilowatt and would generate significant heat, burning smells, fire even.

I cannot imagine what normal load would draw this amount of power. The biggest load is the fridge, which at 96W would draw 8A, but this should not be connected, unless the van is mis wired. Even so it is nothing like the 55A draw that at face value you are experiencing.

I would question whether the battery is sound. If it is at its end of life it may have lost all of its capacity. Batteries normally last 5 years if they have been kept regularly charged. If left in a state of discharge, they deteriorate rapidly.

Take the battery off the van, charge it, then put a load on it and time how long it runs for. A car headlamp is around 48 W so will draw 4A from a 12V battery. This should run for 110/4 = 27.5 hours if the battery has its full capacity.

Even a much reduced capacity, say 20AH which will run the bulb for 5 hours will still provide useful service, dependant how you use the battery. I have used old car batteries, which can no longer start a car, in a caravan, even thogh they must have been down to 15AH