There are many things involved in charging.. First 2 days with no charge and the RV occupied is a LONG TIME unless you have done a SERIOUS upgrade of the 12 volt storage system..
But the alternator has, as its primary duty, the charging of the chassis battery, leads to said battery are generally very heavy duty, Then you find an "Isolator" and leads from there to the house battery are often both long and smaller.. this limits the Alternator's abililty to provide charge to these batteries. IT WILL CHARGE THEM, if you drive like 8 to 12 hours a day, but it takes a long time to do it.
In fact, Four to Six is kind of the minimum charge time for most batteires, Some can charge a bit faster (Say 3 to 5) but for most its 4-6.
How far did you drive each day?