I would use a standalone charger to recharge the truck batteries while the cables are off the terminals, then check their voltages a few times over the next several hours. If the voltage falls off quickly on one or both with nothing hooked to them, one or both have gone bad (unlikely for both at once, but not impossible). If they stay at a reasonably high voltage, hook them back into the truck (camper line disconnected) and check their voltage again in an hour or so. Then if need be, hook the camper back to the truck and again test battery voltage in an hour or so. I think most likely it's a drain from the camper, but the other possibilities must be eliminated first.
