Mako Kupo,
The only additional cost of using 24 or 48 volts is adding a dc (48 v) to dc (12 v) converter capable of running the minor 12 volt loads in an RV.
A few benefits are smaller wiring, an inverter that doesn't have to work so hard and no worries about balancing parallel batteries.
The disadvantages (it is always a trade off) are that each cell has to produce all the watts needed. That may cause them to exhibit greater voltage drop. If this is a problem at 48 volts, then going to 24 may be worth consideration.
However this is all moot as you now have invested in a 12 volt inverter capable of running your RV to your needs level.
I think LI jars are wonderful. It is just the cold that keeps me from them.
May I ask you to list the equipment you chose for the RV?