If you need something that can pull a trailer with a truck on it, best to think along those lines also. A car isn't going to fit the bill there. But a truck is also impractical as a family hauler.
So it kinda looks like you're looking for 2 separate vehicle here.
Also, it looks like you're asking for something to get pulled over in again.
There is no reason at all that you need something quick/fast to haul the family. This is a place you want room and comfort, and something that you won't go broke filling up.
I forgot what the Flex was 'til just now when I looked them up.
Not a truck for you IMO.
If a SUV is what you're looking at, maybe the Edge would be a better option.
But really I'd buy 2 vehicles. A Fusion and an old truck to haul the II.
My final decision would hinge on the cost of insurance on a Edge vs a Fusion and older truck.
Don't "think outside the box".
There is no box.
Do it correct, or do it twice.