The system you describe and show in the photo is what we do, except I do nothing with the batteries except dust them off - whether on camping trips or in at home on storage. They've remained right where I installed them almost 9 years ago.
We keep the RV plugged into a 20 amp outlet continuously while it sits in the backyard - with the battery connect solenoid switched ON almost all the time. I turn the battery connect solenoid off in hot weather so as to not risk evaporating water out of the AGM battereis then. We like the RV to be "always ready" for: Sleeping in occasionally at home, use of it's refrigerator for stick house refrigeration backup, running of the RV's roof vent fan to keep air circulating in the RV to control heat buildup in the summer, running of a small electric heater on a low setting during cold weather, etc..
Our Ford's 130 amp alternator brings our AGM battteries up to full in 4-5 hours of traveling, as indicated by the coach battery bank ammeter I have mounted on the dash. It would take longer if they were wet cell batteries. When the coach AGM batteries are down, the alternator will supply up to 50 amps into them briefly, even when idling the V10. For longer time periods, the alternator supplies 20 to 30 amps into them for awhile as we go down the road. The alternator's charging voltage seems to vary a lot with temperature of the air - as I can see while monitoring the coach's 12 volt system with a voltmeter mounted on the dash. I can see the approximate voltage output of the alternator while driving and I've seen the alternator hold at up to at least 14.4 volts in cold weather and as low as around 12.9 volts in scorching summertime heat. So far, it seems a perfect match to what is recommended for our AGM batteries in all state of charge conditions and at all outside temperature conditions. Ford and/or Winnebago seem to have really gotten it right - by accident or with good engineering - regarding this RV charging system. Your Ford alternator should take good care of your series AGM batteries.
Our two AGM batteries are connected in direct parallel (via an after market solenoid I installed) with an upgraded heavy duty Ford engine starting wet cell battery. All three batteries play well together and all are many years old. I installed the non-stock solenoid because I wanted an extremely heavy duty one with silver alloy contacts - because the stock solenoid was beginning to only intermittently keep the coach batteries charged up - probably due to normal pitting and corrosion of it's copper contacts. I discovered the solenoid problems early-on after arriving at campsites with the coach batteries not up to par, and that's when I changed out the solenoid and also mounted the ammeter and voltmeter right on the dash - so that we would never be surprised again with weak batteries when they shouldn't be. BTW, having a voltmeter monitoring the coach's 12 volt system on the dash tells you immediately if you've forgotten to turn back on the coach battery disconnect switch after turning it off to keep the refrigerator from igniting while gassing up. We like to make sure the refrigerator is on all the time - with no memory accidents - as we carry a lot of fresh food and veggies with us on RV trips
Since our converter's output is 13.6 to 13.8 volts, I chose a couple of 12V AGM batteries with a recommended float voltage of 13.5 to 13.8 volts so that I would not have to spend another $150-$200 on a built-in multi-stage charger merely to have a float of voltage at the common value of 13.2 volts, as required by wet cell lead acid batteries. What happens is the AGM batteries also charge up fairly fast with this same converter, too, which would not be the case with wet cell batteries. So I guess you could say that I take care of our AGM coach batteries with 2-stage charging - the alternator provides the boost voltage sometimes (whenever the V10 is running) - and the converter, sometimes along with an external Sears charger - provides a fixed combination absorbtion/float voltage the rest of the time. This approach only works because the extremely low internal resistance of AGM batteries allows them to accept more current (than wet cell lead acid batteries) at any applied terminal voltage above their intrinsic at-rest voltage.
Sometimes when drycamping and on generator power, I supplement the converter with the Sears charger to raise the terminal voltage a bit and increase current flow into the batteries - similar to what you're doing in your photo. I don't have to get at the coach batteries (they're under the step) to use the Sears charger on them. I just attach the charger's alligator clips to the terminals on the easily accessible Onan generator starting power lugs that come directly, via large cables, from the coach batteries. It's easier to open the Onan cabinet than it is to step over an open battery compartment under the step while they're being charged. When drycamping, I can use this attachment method for the Sears charger while using the Onan to power both the converter and the Sears charger, or when using our portable Honda generator to power both the converter and the Sears charger.
