charging of 2 camper batteries with truck alternator?

That is good wish, but not reality.
I can do guestimate only, but I think 130 amp alternator at idle can deliver +- 40 amp.
Double camper batteries deeply discharged can take hundreds of amps.
Engine starts, trailer charging relay clicks and the truck system has huge voltage surge.
You better check how much new ECU cost.
Most of us will never have the situation, but potential can be disaster.