The OP did not come here seeking sympathy for the plight of her hard working agm batteries, but solutions to recharge them. She is not in a large RV, or towing a fifth wheel, or towing a trailer, and space and weight are big considerations.
There is also an option of using less electricity, by not using battery power to make coffee or cook. I know lots of people have aversions to cooking with propane in a small vehicle, but adequate ventilation alleviates those concerns, at least for me.
In this fulltiming lifestyle we have 3 main charging sources available, grid power via the grid or a generator, alternator, or Solar.
We do not know the vehicle platform of the OP but it is a Van or a MiniVan, and we don't know what specific alternator is in the vehicle, nor how well it can stand the task of being forced into a job it was not designed for.
Generally it is recommended to use all charging sources available to keep the batteries in the highest state of charge as possible at all times.
The MSW inverter on the engine battery powering a regular 'smart' charger obviously works, but can it work as well as if there was a thick copper conduit between alternator and house bank? It depends on the alternator and the vehicles voltage regulator. Factors we do not know and can only guess at.
Say the VR allows mid 14s to be held, and some 2awg cabling between the two allows the AGM house battery bank to drink all it wants from the alternator, how well can the alternator handle this increased load it was not designed for? We do not know, and can only guess at it. Many apparently think it will vaporize instantly, cause a black hole to develop, and swallow the earth whole.
How difficult it it to replace an alternator on the OP's platform, and how expensive is a reman'd alterantor? We do not know. But could it be cheaper to kill an alternator prematurely than kill a pair of AGM batteries prematurely? Very possibly.
The OP has some physical issues so that she won't be installing solar on her roof by herself. The labor to do this job, and how most paid installers do halfass jobs using halfassed wiring, is not a desirable route, though Solar itself is great at silently getting 80% batteries up and near to 100%, a job the alternator is Not good at, and neither is a grid powered charger hooked to a generator or a MSW inverter.
Getting the batteries to a true 100% IS very important, and Solar is a great way to do this, however solar is low and slow, and AGM batteries seem to require higher charge rates when deeply cycled. So some high amperage from another source to get the batteries near 80%, then the low and slow solar can take over and try to top them off and keep them from discharging during daylight. This is a good method.
Running a generator to get the batteries up past 90% state of charge is also wasteful of gas, and annoying to listen to, or smell.
So to the OP, I'd recommend investigating the price of a new alternator and the labor to install it, and compare that to the price of a new set of batteries. I certainly would not use a MSW inverter on engine battery to power a battery charger on the house bank, in a Van, unless the vehicles voltage regulator is too timid to try and get the batteries to the mid 14's, or too timid to allow it to stay up at or near that level where max current will flow and do the most good for a depleted battery.
Solar is a great solution for many, but not all, and those for which it is not a good option, are most vociferous, and want everybody to agree with them. Same for the people who love solar and want everybody to do the same as them.
Some people love generators, others despise them, and those who pollute a quiet and clean environment by running them often.
You can't make everybody happy all the time, but consideration for others in the vicinity seems to have gone out the window too in recent times too, as if narcissism is a character attribute instead of a character flaw.
I use between 35 and 65 amp hours each night in my Van. I have 198 watts of solar on my roof, and park in the sun more often than not. My alternator is thickly cabled to my batteries, and it can easily be maxed out by my depleted batteries. If either of my batteries are depleted, there is no way I will not take advantage of this huge charging source.
Even if I use only 30AH overnight, an easy task for my solar to replensih the next day, if I drive in the morning, the battery gets everything it wants from the alternator as I drive from A to B. I've noticed these higher amperages, even briefly, allow the battery to hold higher voltages for longer during the next discharge cycle, compared to if the solar alone brought them to the high 90% range on its own.
My alternator is regularly maxed out and has been so for the last 8 years. I have no fear of killing it as I can replace it myself in 15 minutes, and I have a lifetime warranty on it from Kragen Autoparts, but do not know if Oreilly's will honor Kragen's warranty. Anyway a reman'd alternator is about 125$ on my vehicle, and my flooded deep cycle house battery ( not a marine or dual purpose)is $165 minimum. So for Me, in my rig, the alternator is not going to lead a creampuff pampered life and just replenish the engine starting battery, but will be whipped by a depleted battery over thick cabling, and I will be there every night whipping my battery down to the 70 to 50% range each and every night, and perhaps even lower when Peukert and capacity loss are factored in.
And I will use each and every charging source available to get that battery as close as possible to 100% before the next discharge cycle begins. But I will not use a generator, and in fact I could plug in anytime I want and not even cycle my batteries, but I want my solar to have work to do, I want my batteries to be worked, and I do not want to rely on the grid at all.
But When I do, I want my grid powered charger to do the best job possible, and through this forum, I'd learned the best way to do this, in my rig, with my intentions, was with an adjustable voltage power supply, to prevent premature efloatulation. That hideous and lawyerly ending of absorption voltages well before the battery would like that is the bane of all automatic charging sources.
So Naio, I'd recommend researching your alternator, and perhaps posting which one it is. Mexwanderer is intimately familiar with alternator design and can make a guesstimate as to how well it can handle a severe duty cycle from feeding depleted AGMS regularly. Knowing how hard it is to replace, both in labor and in unit cost, and weigh that against a new set of AGM batteries. Solar is great, but if stealthiness of your rig is desirable, solar panels on the roof detract from that, but not nearly as much as an idling vehicle with an inverter and cordage hanging out of the hood, or a stinky generator noisily allowing your 30 amp charger to underfeed the AGM batteries, which could likely accept 3 times that amount for 2 hours when depleted.
Also keep in mind the low and slow charge pattern of Solar is Not ideal for AGM batteries. They would prefer a higher am charging source when heavily depleted. Heck, all my flooded batteries seemed to like this too.
AGMs also differ in their recommended charge rates, some saying no more than 30% of capacity, and some others saying no less than 40% when deeply cycled, so knowing what AGM's you have and the manufacturer recommendations is also very important.
Any and all charging sources, whenever possible. Maximizing their effectiveness will maximize your battery life. This can be taken to extremes, so weigh those extremes against replacing the batteries a bit sooner from a less ideal recharge regimen.
Everything is a compromise, and always will be, knowledge is power, and the decision is yours.
