Ok...I have a couple of threads going on a couple of forums, and have learned a 1/2 ton about figuring this out in just 24 hours.
First off, I took my truck to a CAT scale today. After doing some re-math before I went, if you can believe this, the actual weight on the scale was within 1 pound of my new calculation.
So what I learned by this is that I was completely wrong about the 1200 pound tongue weight. In fact, on the other forum, my seller chimed in and helped me figure some of this out. Partly that the advertised TW of the trailer in question is 775 lbs, and after he weighed his truck with the trailer, he calculates the actual TW at 745.
My truck weighed 5640 with a full tank of gas, no cargo and no passengers. Add 550 for me and my other 3 passengers and 745 for the trailer tongue, that gets me to 6935. Subtract my 7000 GVWR, that leaves 65 pounds for cargo. Which for me might just mean to put all my cargo in the trailer as we tow it.
What makes me feel better about this, is that the seller mentioned that his vehicle also has an identical 7000 GCWR, and his truck weighs nearly what mine does. So pound for pound we are even, except he has one less passenger (100 pounds difference). If his truck can handle it, then I am sure mine can. And he is from around here and used to go to the types of places I plan to.
I think I am in a better place when it comes to vehicle weight capacity...do you agree?
The next step is towing the trailer...