Batteries

I am assuming its the house batteries you are talking about and it has separate engine starting batteries.  like I mentiond in another post lifepo4 in motor homes can be a bit more involved but not much.  you want to keep your starting batteries lead acid and aside from your two LiFePO4 batteries you are buying, brabe a dc to dc charge also and use that to charge the LiFePO4 batteries from the engine as lead acid and Lithium require different charge profiles.  you will probably have to look at the converter also.

as for batteries there are some cheep brands that are put together really well and preform well, like redodo.  I believe your motor home came with two and has room for 4 house batteries, so before you buy any sit down and figure out how much power you need.   what I do is have enough capacity that I can do a normal trip with out worrying about running out of power, so if you normally do 3 days trip, when you know your usage over 24 hours multiply that by three and that how much capacity you need. 

the other thing to keep in mind is peak current, if you have a inverter what size is it and how many amps can it draw.  then you get the number of batteries so your BMS discharge capacity will handle that.  so for example I have a 2000 watt inverter in my 5th and that works out to somewhere around 175a if loaded up with the inefficiencies, so I would need at least two batteries if they only had 100a bms's in them, or one larger one if it had a 200amp bms.  

the other thing is the space you have available.  you could in theory get four smaller batteries or 2 or 3 larger ones and end up with more available power.  it all depends on how you use your rv.  for example if you drive long days getting somewhere the extra AH to power a residential fridge during the trip or what not might be how you want to go, if you boon dock a lot and your like me and hate generators then lots of power is the best way to go.  remember that average camping trip method I mentions of siding battery banks, mine id 9 days and I have solar that can recover all that in about 2 days so I don't have to worry about generators and I don't have to go home if my solar breaks down.  granted that's harder to do if you camp like you live at home, but if your like me and only use 120V power when you need to its not bad

Most retail lithium 12v batteries are going to be capped around 100-200amps (continous vs peak load) before he BMS cuts power. If this is for the starting batteries, that's not viable as a big diesel engine can ask for 800-1000amps or more.

If it's for the house batteries, lithium is great but the charging gets more complicated. Lithium and lead-acid want different charging voltage and amperage. So if you want the alternator to charge the house bank, you need a separate charging circuit that is able to take the power off the alternator (or thru the starting batteries), adjusts the voltage and feed it to the lithium. If you put in a good size solar array, it is possible to simply disconnect the house bank from the alternator side of the 12v system (or if you never boondock, but if you are always on shore power, you don't gain much of anything going to lithium). 

motor homes are always the hardest to do, while the LiFePO4 batteries are very appealing for the house batteries you do not want them for the starting battery.  this creates a mixed battery chemistry in the motorhome and the easiest way to deal with it is to remove the charging line from the house batteries and put a dc to dc charger at the house batteries that has the power supplied from the charging line, or directly from the starting battery if you want to run a new power line for a larger amperage dc to dc charger.  also look for one with a ignition sense.  this makes it so it won't pull power from the starting batter unless the engine is running so it also acts as a battery isolator.