monkey44, please do not take offense to this post, but it is not as simple as you see it. The reader inside your TC really only gives you a hint as to the state of charge in your battery. It really is of questionable value in my opinion. Unfortunately, it cannot be explained without being technical to some degree.
When you say "... my truck can charge my TC battery in one hour - like it did today, after three days of use in dry-camping.", it does not give us enough information. Using that experience, I agree with you that you do not need a generator to bring your batteries up to the reader inside your TC. I still do not believe the batteries are fully charged in 1 hour. It is not instant, but I believe you will greatly shorten the life of your batteries.
Using a volt meter, how many volts do you believe a battery should show to be fully charged?
Wayne