Your approach is very much like mine was... I went for the larger PD9260C smart mode converter/charge as my battery bank is three 85AH 12VDC Interstate batteries (255AH). Later on I am wanting to go for two separate 300AH battery banks. One to be located on the trailer tongue and the other one located in the bed of my truck.
You might be just a tad below the rule of thumb of having charge capacity of 18-20AMPS per battery available from the PD9245 charger... If each of the four 6VDC batteries demanded 18AMPS of charge current that would need to be 72AMPS of charge capacity. 6VDC batteries rule of thumb may only be 7-8AMPS per battery charge demand when you hit them with their BOOST mode charge voltage of 7.2VDC.. If that is the case then your PD9245 is really only looking at two 12VDC batteries when you consider two 6VDC batteries in series is one large 12VDC battery??? If this is the case your 45AMPS of usable DC current is just fine for your four each 6VDC GC2 batteries. You are apparently already getting to 90% SOC in three hours time using your 1KW generator.
This higher charge will only last a few minutes and the batteries will then start dropping down in demanding lower DC current during the BOOST charge cycle. My three batteries in parallel demands 52-53 AMPS of DC current for the first 15 minutes or so of boost charge then drops down to around 8AMPS by the end of the two hour BOOST mode cycle. To understand this better you need to measure how much current is being demanded from your 45 AMP charger when in the initial BOOST charge mode. If they don't get their required DC Current draw this would only mean you will need additional time to get a 90% charge state.
My three 85AH 12VDC batteries in parallel gets to their 90% recharge in the three hours smart mode charge run just fine.
What I don't have any documented experience with is what happens if I don't run my batteries down to 12.0VDC SOC before recharging. i.e. what happens if I just drop my battery bank to 12.2VDC and then hit the manual BOOST MODE charging. How long does that take to get back to the 90% charge state. This may be where the SOLAR PANELs really come in handy keeping your batteries topped off and never really need to use the full BOOST MODE charging technique.
Again I like your idea of mastering the camping off the power grid using just batteries first and then later on adding solar panels to supplement the charging process... You will know what to expect doing it this way. For us the generator method was the only PLAN B thing that will always work no matter what the conditions are.
just my thoughts
Roy Ken