Infrared heaters do not heat the air and they don't move air around. They warm up the objects and people that infrared "waves" hit which in turn also radiates back into the room.
There are various types like wall mount, ceiling mount (flat panel) and recessed (lamp bulb tpe). They are a little more efficient generally since you don't heat up all of the air in a room to feel warm.
The lamp bulb type work great in a place like a bathroom as the rooms are small and you feel the warmth when under them but would be too tall for an RV. A ceiling mount flat panel is likely too large in area for an RV. A wall mount *might* work but you'd be too warm near it and cold elsewhere in the RV.
One important thing to consider is that thermostats don't work very well at all with radiant heaters because they do not heat up the air. Often, they are simple connected to an on/off switch.
Radiant heaters work well in places like big warehouses with high ceilings where you want to provide heat to say workers at a counter.
I suppose if you have few options and you just want to keep somewhat warm on a few outings in the cold season, you could opt for a portable plug-in radiant heater and just put up with being too warm or too cold. But you'd want to be very careful that the heater doesn't fall over or get aimed at a wall which could create a fire hazard.
Personally for a permanent solution, I'd suggest some type of heater or furnace that has a fan in it that will push some air around. In a long/narrow RV, you'll probably not going to get evenly heated from end to end but it's going to be better than a radiant heater warming up just what's in front of it. For occasional use or supplemental use, I'd suggest one of the small ceramic heaters or oil-filled fin types.
BTW, I'm an electrical engineer and used to design electric heating systems in all sorts of buildings so I kinda still know this stuff (now retired and I don't keep on top of this anymore). FWIW, the recessed elec. ceiling heater (see my post) I installed cost about $250, all inclusive, for parts - heater, relay, LV transformer, thermostat and a little wire. The hardest part was the 8 hours or so I spent installing the heater and wiring.