Personally I'd opt for the heavy duty because they won't impart a hard as a rock ride to your conversion van. The "comfort" name brings up images of a mushy floating sort of road feel, not something I prefer when pushing one of these billboards down the highway.
I do believe Bilstein has a ride satisfaction guarantee that allows you to exchange one valving for another if you're not satisfied. Please confirm that with Bilstein though, get their comments first.