Going into Float voltage (13.7), doesn't necessarily mean the batteries are fully charged. Would suggest you check the actual state of charge when it goes into float, or at some point shortly thereafter. I'd disconnect one of the battery cables and let it sit unused for a day. Then use your hydrometer.
Another thought, try turning off all the loads in the trailer before you check for the State Of Charge as indicated by the GoPower. The GoPower converts the voltage level to the percentage you see, not all that accurate. If there is a load the voltage will be lower then it really is.
The GoPower manual is pretty lousy.
FWIW, I use about 10A a day depending on if I need the furnace.
