charging of 2 camper batteries with truck alternator?

Not sure what you expect from Ford, GM or RAM. They will give you the alternator output rating and you can check the 7-pin charge line fuse rating.

You are basically plugging in a custom accessory that you need to engineer to your own specifications. If you need more power than the alternator rating you need to order the HD or dual alternator. Or if you want more power than the 7-pin connector allows you need to pull your own wire. No manufacturer is going to custom make a charging system for an RV.