Ok I did this sketch while sitting at Burger King this morning (always bring a pencil, my graph pad, and a protractor). I reworked the A-frame to 50º (since couplers are either for straight 2x2 or a 50º angle).
The main frame will be 4'x8' (with a coupe of 6.5' crossbars) and the trailer body will curve up at the front, but still have an overhange of 15"
So does this look right or should I ad a little more length to the tongue?