The gray wire bundle is the thermostat wire. Not all of the wires would have been used, even if the camper had been ordered with an air conditioner. That’s just the cable Lance chooses to use.
The red and white wires hanging out with the gray wire I’m betting are 12v DC, for powering a Fantastic Fan for example. The fact that the red wire is capped suggests that it may be a live circuit. You should put a meter on it and check. I’d don’t think your new air conditioner is going to need 12v.
As for what to do with those, I’m betting that once you get the new rooftop unit, you’ll find that there’s enough space around the perimeter of the ceiling cutout to stash those wires.
The three capped wires hanging out of the box are of course 115v AC for the air conditioner. The new air conditioner may have a pigtail that will reach into the ceiling box, or as you said just make your own.
:):)