I have a 2010 E350 6.0 diesel and used 'Roadkill' and 'Dynamat' (different products) in the doghouse, inside the front door panels, on the front floors, and on the floor behind the from seats. I also use rubber horse stall matting for the floors throughout the van (no carpet). This combo works pretty well. I roll with Nitto Terra Grappler G2s. They are not the loudest tires on the road, but they do hum a bit. Highways at 'normal' speeds are not a problem.
2010 SMB Ford EB E350 4x4 6.0L; 2003 Toyota Tacoma SR5 4x4 (Dual Cab); 1992 BMW R100 GS/PD;
1994 BMW R100 GS/PD