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