There are many multi channel dashcams, the problem however is the rear camera which are wired, well getting it out the back of a large trailer or camper is next to impossible.
Your best bet will probably be to put a regular 1 channel dashcam in the rear window of the camper if it have that.
There are no dashcam that have remote cameras that connect with wifi, or there is one ( i have it ) but i for sure can absolutely not recommend that in its current state, and even so the rear camera well us kick starter supporters have not even seen that yet, and i very much doubt we will this current year.
You could maybe put up one of the small battery CCTV cameras like ARLO / WYZE and what not they are called,but i am unsure if they are actually on all the time, though if they use motion detect, and are put on back of moving vehicle i assume it will, question then is how long will a charge last.
There are also wifi cctv network cameras, that i assume you could connect directly to with a phone / laptop, most often using 12 V power, and also often have a slot for a memory card for local storage.
I do run network cameras in my apartment, but all wired ones, have never tried a wifi one as i do not like wireless