charging of 2 camper batteries with truck alternator?

If I understand you about the solenoid on the hot truck wire, I have no power in that truck side plug when the truck is not running. I think that solenoid is part of the camper package. I am waiting for Christmas and Santa (my wife) to put a 140w system on the roof! I am having a compressor put in for my air bags in a few weeks, and I will ask the installer to check the charging line. Thank you for the reply!