RV systems are simple systems that are made complex by combining 120V, 12V and propane to run them. I don't know of any course that would cover all the systems of various manufacturers.
This forum is a good resource but you have to remember that anytime you are getting advice from a public forum there will be a lot of bad information. All though most have good intentions you working on your new(er)RV is not the same of someone who did a repair on their older unit.
When you read enough of this forum you will start yo recognize the members who know what they are doing and the others who think they know what they are doing.
Make sure your settings will allow you to get private messages from other members so others can contact you.