If the connection to the batteries from the converter is bad, either positive or negative, the batteries will not show a high voltage when charging and will not get a good charge.
It sounds like you have done everything right, but you need to have a battery voltage meter (mine cost $3 from China). That will show you what level your batteries are at.
If you are charging by plugging in the camper with Honda 2K 120 volt power, the converter should put out 13.6 volts, and you should see that at the batteries. If you do not see that, check right on the converter output terminals. If you see it there, check the tightness of the wires on the converter terminals, both the positive and the negative wire that feed the battery.
In my case, I was plugged in to power, and the negative wire on the converter was so loose the converter was putting out full power but the batteries were not getting any of it and they were getting lower and lower in their voltage.