Switching to Lithium Ion Battery Bank?

Without getting too long, please do a lot of research into Lithiums before trying to do it on the cheap! There are several different chemistries, some fairly safe, some very unsafe (think Samsung, Hoverboards, etc.). Packs do not come in "12v" configurations, but around 11.1 to 14.8, with variations due to specific chemistry. You must have a charger specifically for them, that can balance each cell in a pack (3-4 per pack). You cannot run them down to 0, that kills them right away. If not used for a moderate length of time, they must be partially discharged to a storage voltage, or you greatly shorten their life. They do not tolerate cold at all. There is a lot of babysitting involved in owning them, and if you neglect them, there is a moderate to good chance of burning up your RV with some of them. The old Spiderman saying holds true here also: "With great power comes great responsibility".