Over my time I have seen the changes in methods used to charge caravan batteries. It was around the late 60's early 70's first got involved, this is the time of the Lucas ACR alternator and a firm called Durite who are still around today made a replacement rectifier with 9 of the same sized diodes, so I used three extra diodes to the field and used the three in the rectifier as a second output, this charged the second battery for a caravan far better than the proprietary methods with blocking diodes and relays.
I found the 0.6 volt drop with the blocking diode resulted in both batteries not being fully charged, OK with marine applications where the 440 regulator had Hi, Med, Lo terminals but not with the built in regulator of the ACR alternator. The relay did work, but the vehicle battery had less cable to it to the caravan battery.
Until the DC to DC inverter hit the market, there was no really successful method of charging the second battery, the second battery needed stage charging to have any hope of fully recharging it, and even with stage charging it would take 12 hours and we tend not to tow caravans for 12 hours.
Even the canal boats had problems without stage charging, and they could easy run 8 hours.
The solar panels had the same problem, the MPPT controller however does help, the major problem with a stage charger is the load can stop the stage charger dropping into the final stage, so can over charge the battery. But also with the old solar control (a simple zenor diode) morning and evening output was very low, the method around this was to vary the solar panels output voltage, so as to gain the most output, but to charge a battery the ideal voltage is not the same as the ideal voltage output of the solar panel, so an inverter is used so the panel voltage have vary through the day, but battery voltage stays constant.
Clearly the inverter uses some power, so this is only done with the larger panels.
Deep cycling lead acid means a long recharge time, put a energy monitor on a mobility scooter battery and before fully recharged from flat again it takes around 8 hours, and this is when put on charge as soon as the scooter returns home, and with AGM batteries, if batteries left a few days, then 12 hours again.
To get around the time it takes to recharge lead acid the narrow boat users look at using a hook up once a month to fully recharge the battery, and with your situation you would likely need two lead acid batteries and alternate them so each month they can be fully recharged.
So in essence all the solar panels are doing is reducing the size of lead acid required.
We do have the alkaline battery, started with the Nickel Iron, these can charge and discharge faster, today we have the Li-ion battery, again able to charge and discharge faster, and most the garden solar lights have AA cells in them, the charge control is often built into the cell, and these can recharge in 12 hours. But at the moment around 8:30 am to 3:50 pm looking at my solar panels so around 7 hours max. Just when I need lighting on my drive, the sun light has dropped to a level where not going to recharge the battery.
So assuming using lead acid then all the solar does is extend the time between needing to swap the battery and take it to be recharged. Or at least swap which is being used as well as being charged, but that means manually swapping batteries, so if the battery needs swapping anyway, is there any gain using solar?