Can't comment so much on washboards but I have no worries. I've put 50k on my LWB medium roof Transit so far and the thing rides and handles like a sedan. Just go drive one. It's really amazing for a one ton van. I routinely haul 3-4k in mine for work and it still handles and goes fine, just stops slower.
I had a major mishap in mine a week or two ago. Lonely interstate at night and I was staring down at my phone running about 75. All of a sudden my eye caught an old pickup in front of me putting along about 50 mph on the interstate at night with those old dim domestic truck taillights (think old S-10 or the like, small dim lights). I didn't even have time to brake, I just grabbed the wheel and turned, at 70 plus, knowing it was ram him in the rear or chance it in the grass median probably rollling my van. The Transit handled it! It simply moved over a lane and smoothed out. After a quick change of underpants and some healthy screaming at myself for being such a dumb *** I just rolled on down the road.
Simply put, no further worries about how the Transit will handle any upsetting road surface or maneuver.
