Believe it or not ductape, some of your issues have to due with how long you plan on RV'ing With me I'm afraid it's a few years more and that's it. Cycling an AGM down to say 40% of capacity will knock perhaps 10% of its lifespan but that 10% added capacity can be tempting in a borderline situation.
Yours IMHO is a perfect post, it states what you want and why. Kudos.
Alwsys design on "worse case". 125 amp hours = 375 amp hours and you need a battery system with double that (750 amp hours for 50% discharges). From there you can start backpeddling because you say your pig-out days are few.
Your stated average of 210 amp hours of consumption means of course 420 amp hours of batteries. Four group 31 Lifelines seem like a glove fit capacity wise.
If you run your generator "anyway" for hours on end then the following point is moot.
Those four lifelines can swallow a 150 ampere initial charge rate without so much as a burp. If you are going to split up the batteries, keep this in mind. You are going to have to measure with string the accurate cable length, then consult a chart to determine correct length. Beware of single length wire charts, the negative has to return and this is going to DOUBLE the wire length.
IMO your so-far unaddressed issue is having enough charging power. BFL13 has proven to be highly experienced in this department and I hope he chimes in.
Your solar is going to help but I wouldn't stake a trip on guaranteed solar output delivery. It simply means you can run the generator for a shorter length of time and that's it.
Make sure your charger's profile agrees with what Lifeline specs recommend, ESPECIALLY float voltage while plugged in at home.
I am shortly going to take possession of a Lifeline group 31 thanks to an unforeseen miracle thunderbolt from heaven. I have no choice, it has to go under my bed. So, an LCD monitor for me is a must. One that can be seen by twisting my head while in bed. This is a shore-power setup so recharging is going to be gentle as can be. But I may have to, on occasion, cycle it down to 20% of capacity. For those readers about to scream bloody murder, A fan is going to exit any possible slight venting and carry them to a house exit fan intake area. If I lug the monster 150' to the generator shed 2 40 amp MegaWatt chargers are going to feed it for a period that agrees with the recharging time needed for the 24 volt bank. I need my yero (son in law) to smooth the rough path between house/RV and generator/battery/inverter shed. Why do I sleep in the house? Try a 5" thick memory foam mattress!
If the Rolls' bank needs 2 hours at 500 amps then the Lifeline has to recharge as much as it can in that two hour period. The 12.5KW Kubota is not going to laugh and dance and eat lobster while powering a 1200 watt load.
