I haven't done it on an Anthem, but looking at the wiring diagram provided by Entegra it should be fairly simple to do with two switches. One for the top shelf of batteries and one for the bottom. Using two switches should simplify the installation and minimize how many new cables you need to make.
There are two approaches. You can add cutoff switches for just the inverters or for the entire battery. In either case you should only switch the positive conductors.
Switching just the inverters is easier and should only require two new cables. The inverters are by far the highest vampire drain (even when OFF) and will take your batteries down to about 50% in 1 month from a full charge. With the switches in place and the inverters truly off, your only drain will be the See-Level, Fire/Smoke/CO/Propane sensors and some other low level stuff, but you can pull the fuses for most of those. Another benefit of switching just the inverters is the current for high load items like the generator starter and leveling jacks will NOT pass thru the new switch.
Switching the entire battery will shut everything down and maybe some stuff you don't want like radio settings (?? don't know, those items may be fed by the start batteries ??). The wiring gets more complex too. For example, you will need to move the inverter cables from the batteries to the off side of the switch lugs - that can present some physical challenges due to the lug and wire size.
I wouldn't worry too much about overloading these switches. I typically used the BlueSea products
in my marine work in applications where engine start current was passing thru them. Other brands are fine too, just check the ratings. Even the smallest BlueSea m-series switch has a 1500A 10 second rating, a 500A 5 min rating and a 300A continuous rating. You are not cranking the engine thru it and are unlikely to ever see continuous current of that magnitude. For a little extra margin of safety go with a switch like the BlueSea e-series (350A continuous, 2000A 10 sec). You do not need a switch with an Alternator field disconnect. The Blue Sea 6005 or 9003e for example.
See the attached diagram. To add the cutoff switch to the inverters find the red cable on each shelf of batteries that go to the inverters - those cables will go to the "Magnum" labeled Class T fuses in the back of your battery bay. Find a place to mount the switches where those cables will reach and connect to the appropriate switch lugs. New cables will be needed to go from the switch back to the battery POS terminals. Use at least the same size cable, if you can't find the 3/0 go up a size to 4/0. Use closed end tin plated lugs and seal the crimps with adhesive lined heat shrink. I think all lug holes should be 3/8". If you don't have a heavy duty lug crimper these guys
are very reasonable for custom assemblies and you will get high quality tin plated marine cable and lugs.