It's definitely not a power/battery issue if two separate detectors with two separate power supplies were both going off.
Somehow, CO got into your camper and set them off. Tread carefully because CO will knock you out before you even know something is wrong, and anyone that comes in after you to rescue you may also be overcome.
It could have been the truck. Just because the alarms didn't go off immediately doesn't mean anything. Fumes don't travel instantly. It might be an hour or two before enough fumes infiltrated the camper to set off the alarms. For that to happen, though, you'd need some sort of ventilation pulling the outside air into the camper.