I just finished my off road frame. My first suggestion would be make it at least 9'. That extra 1' makes a huge difference in the galley. Second, I did not get all worked up about the tongue angles. I just laid one on the frame, adjusted it where it looked right, made at least 3 connection points, and marked it. Then cut two. Worked great.
I put 35' tires on so is just a bit heavy at 570 lbs with 25" clearance. That will settle after the build.