My namesake, the guy to my left in my Avatar, believed in primary safety and not secondary safety. In essence he believed that the vehicle should be capable of avoiding hazards with safety and stability. His cars were all designed with stability and handling - an original Mini for example could still give a modern sports car a good run for its money with only 1275cc.
In fact he recommended fitting a line of carving knives along the dashboards of cars to encourage drivers to drive more safely. Although this is extreme it seems to me that some cars and owners have gone to the other extreme - huge cages of metal to convince themselves into being safe, when actually they might not be - see SUV crash tests vs. hatchback ones for example. All this means is that some start driving unsafely, using phones whilst driving and so on.
All that tapped if you are looking to improve FE then the obvious ones are listed in the 100+ tips thread which is a great start. The other key one would be P&G especially in something as lardy as an econoline - funky name for something so big and thirsty but hey, I'm British
Being and on topic though you can probably take advantage of the weight on hills with P&G and maintaining momentum. I'm thinking that weight is going to be more key than aero with something like this battering air out of the way with all of that mass. You could take steps to reduce weight if you can - spare seat removal for example, fewer tools, no golf clubs except on the way to the course
You could look at aero. Your idea of sealing up the front of the car seems extreme but you could just look at sealing up parts using the old coroplast / grill block / tape methods described in various threads - that way you could test the most effective methods. I would also look at the side mirrors too.
Good luck with any changes you make and above all keep a log of fuel usage so you can see what works and what doesn't.
