If there is any kind of drain on the battery the low wattage solar panels are pretty close to worthless. Let's do the math.
A 12 watt charger puts out about 1 amp at 12v. On a good day the total amp hour output will be about 3 times the nominal wattage, or 36 watts or 3 amp hours.
A Group 27 Battery has a capacity of about 75 amp hours, of which half are useable, so there are 36 amp hours available for use (taking a little liberty with math to keep the numbers simple). So, if the batter was used to 50%, it would take 12 days of no use to recharge the battery to 100% if battery charging was 100% efficient, which it is not. Batteries do not like being in a partial state of charge (PSOC), the longer they are in a PSOC the harder it is to recharge them and the batteries age faster, it is a downward spiral to the battery recycling center.
For a FLA battery, the charge should be at least 10% of the batteries rated capacity, or for a Group 27, a panel capable of producing 7.5 amps or 90 watts with a good MMPT controller.
The alternative is frequent battery replacement or a modern multistage charger and a connection to shore power.