What length Supertruss for an AF990

I just put a 32" on mine and it allows the ball to just clear the back of the bumper...perfect for us. We have a Fox Landing no issues there either.
Can load pics if you like.

You want the ball out from under the camper/bumper. If you get the extension to the end of the bumper, the drop hitch will put you in a convenient place.

Get the 24". No real difference in capacity and the extra turning clearance might come in handy.