RV batteries...how many?

Adding to what has been said, you could along with a 600 amp bank add 600-800 watts of solar. You wouldn't reach self sufficiency, but you could cut your Genny time about in half. And as you put it earlier, you would have another back up to your back up.

based on my limited experience I suggest you run the generator when your are running the concentrator ans/or charging any batteries. I use a portable concentrator when driving and run the inverter to power it and the refrigerator. I have run the generator all night to power the more robust house size concentrator.

reinforce one storage bay, preferably mid-ship. use all-thread rod, or welded angle iron from the chassis/frame to below the bay floor, put angle iron and marine plywood under the bay floor supported by the new supports

stuff that with batteries i would go at least 6 (aka 3 pairs) or maybe 8
this would give 600-800 or more AmpHrs

we had 665 AmpHrs of AGM battery in our previous coach and powered a residential fridge, but it only drew 100w and a 40% duty cycle

the O2 concentrator is the biggest concern and the biggest power user

4*120v 480w, that a 40amp load using 12v battery bank to power an inverter

that only 20 hrs continuous load until dead, or 10 hours (aka overnight) until an 800Amphr bank is at 50%

you could double that to 1600 ampHrs (16*6v) and have 24hrs safety margin
but i think, you are going to need to depend on the generator if you loose power for more than 4-6 hours

traveling and short stops from inverter or genny as needed

parked/camped shore power with automatic inverter switch over when shore power drops out, then switch to genny as soon as possible, don't wait until batteries are low

i don't think you can carry enough battery for 2-3 days of powering her O2 concentrator

The question is how much room for batteries do you have?

The 6V golf cart batteries are the way to go as they will have more capacity than a single 12V. The problem is do you have enough room to add more batteries? Do you have an inverter/converter to run her oxygen concentrator when not on generator or shore power?
You may already know this but.
Converter
A converter is an electrical device for converting 120-volt AC power into 12-volt DC power. Most RVs with electrical hookups will have a converter, since many of the lights and some other accessories run on 12-volts DC. A converter may also function as a charger for the coach batteries.
Inverter
Inverters are electrical devices for converting 12-volt DC power into 120-volt AC power. There are two basic types available: modified square-wave and pure sine wave with the former being the most common and least costly. They are available in sizes ranging from as low as 30 watts up to 3500 watts or more.
Bill

So for the 0.01% of the time I would run the generator. Does the Damon even have an inverted to change the 12V battery to something you can use...120V for the battery charger.

Why do these dups happen again and again. You click the Post Message Button to post and then it shows the dialog box again and the same Post Message Button which makes it appear that you have not done the post or the post did not take. After that, you end up here writing this!
:h

Since you have a generator, that should be all the backup you need. While driving from campground to campground the engine alternator should be large enough to keep the batteries charged. Only if you have a plan to dry camp for an extended period of time (no hookups) would you need to be concerned about battery capacity. You would also need an inverter of the proper size to handle the load and ensure that you have outlets wired for that inverter to allow the use of these products.