RVs that only have space/weight for two batts but still want to run the MW off a 2000w inverter have a problem. Can't do it with two 6s and two normal 12s either really. Hence all the tries with Lifeline AGMs, or other 12v AGMs.
I tried that and the two AGMs couldn't handle it for more than a few years. I was disappointed in that.
So now you can get LFPs, which allow you to run them down to low SOC and still have higher voltage so the inverter alarm does not go off, but they co$t big bucks. It is all about your own scenario with your rig, what you can do with what and whether it is "worth it". (See many posts on how to make coffee! :) )
I made my choice since I have no problem carrying four 6s and that works great, no need to seek alternatives at high co$t.
If you only look at where you can carry your FLAs as your two batt limit, don't forget you can carry AGMs inside at low risk (not no-risk) so that might be the way to get it done at lower co$t by using more AGMs. It is all situational.