So, I used clamps and a 1 by 2 on my circular saw to create this temporary tool.
Then I tested in on the board I needed to cut as shown here,
Looks right. Then using the bed of my pick up truck as a work holder, I made the cut. The board is redwood so that make it all a lot easier. Here is the final result.
A 15 foot angled cut as good as a table saw could have done.
Rick