charging of 2 camper batteries with truck alternator?

Any alternator can loose diodes or have one or more partially burnt. Just like tires they don't last forever. The problem arises while still seeing charge rates okay, yet your system is leaking enough AC ripple to damage sensitive on board electronics.

My concern is the more you ask of your alternator the more wear, like tires, you can still be using them , but with an alt there isn't a clue unless you get a good Volt Meter and test for levels of AC voltage.