battery based on sodium ion (salt)

Their "S line" battery seems the most suitable (or least unsuitable) for most RVs. It's roughly 1' by 1' by 3' high, weighs 260 lbs, and is a 48V battery of around 2.5 kWh at the 20 hour rate. It does appear that the internal impedance is fairly high, so these would presumably not work too well for brief high-current needs like starting motors or inverters used for things like microwaves (when the load is comparatively large for the battery). By way of comparison, this has somewhere around the usable energy storage of four golf cart batteries, with somewhat of a savings in weight.

Their distribution network seems to be very much oriented around fixed installations, presumably off-grid solar or similar alternative energy applications for the most part. It's not clear whether or not the battery is particularly susceptible to damage from vibration or off-angle operation or temperature extremes. If these are not big concerns, I don't see why it couldn't be used in an RV application with the appropriate DC-DC voltage converters and other associated ancillary work. There probably wouldn't be much tangible performance benefit for most people, though, and I assume no great cost advantage either unless one sees a great many charge/discharge cycles.

Edit: Add a link to the spec sheet for the battery.